eki no erebeetaa ga kosyousita node, kaidan wo tukaimasita.

の links two nouns. Here, 駅のエレベーター means the elevator of the station or more naturally the station elevator.

In Japanese, の does much more than show possession. It can also show:

• location/association: 駅のエレベーター = the elevator at the station
• category: 日本の車 = Japanese cars / cars from Japan
• belonging: 私の本 = my book

So this does not necessarily mean the station "owns" the elevator in a strict sense. It just identifies which elevator we mean.

が marks the thing that experienced the breakdown.

In エレベーターが故障した, the elevator is the thing that broke down, so が is natural.

Compare:

• エレベーターが故障した
  = The elevator broke down.
  Focus is on the event/the elevator as the thing affected.

• エレベーターは故障した
  = As for the elevator, it broke down.
  This can sound more contrastive, like maybe comparing it to something else.

So が is the most straightforward choice here.

Because it describes an event that happened before the speaker used the stairs.

The sequence is:

1. The station elevator broke down.
2. Because of that, the speaker used the stairs.

So 故障したので means because it broke down.

Even though English sometimes says because the elevator was out of order, Japanese often expresses this with a past event: it broke down.

故障する means to break down, to malfunction, or to stop working properly, especially for machines or equipment.

So:

• エレベーターが故障した = The elevator broke down / malfunctioned

It is a common word for mechanical problems:

• パソコンが故障した = The computer broke down
• 車が故障した = The car broke down

It sounds a bit more formal or technical than some other ways of saying something is broken.

Yes, often you could, but the nuance is a little different.

• 壊れた = broke / became broken
• 故障した = malfunctioned / broke down

For machines like elevators, 故障した is very natural because it focuses on the equipment not functioning properly.

Compare:

• エレベーターが壊れた = The elevator broke.
• エレベーターが故障した = The elevator malfunctioned / was out of order.

Both are understandable, but 故障した is especially common for machines, devices, and systems.

ので means because, and it gives a softer, more explanatory reason than から.

So:

• 故障したので、階段を使いました。
  = Because it broke down, I used the stairs.

Difference in nuance:

• ので = more neutral, explanatory, slightly softer
• から = more direct, sometimes more assertive

Compare:

• エレベーターが故障したので、階段を使いました。
  = Since the elevator broke down, I used the stairs.
• エレベーターが故障したから、階段を使いました。
  = Because the elevator broke down, I used the stairs.

Both are correct. In many contexts, ので sounds a bit more natural when calmly explaining a situation.

This is very normal Japanese.

In subordinate parts of the sentence, Japanese often uses the plain form, even when the main sentence ends politely.

So:

• 故障したので = plain form + ので
• 使いました = polite main verb

This mix is standard:

• 雨が降ったので、帰りました。
• 時間がないので、急ぎます。

Using 故障しましたので is also possible, but it is more formal or stiff. In everyday polite speech, 故障したので、使いました is completely natural.

Because 使う means to use, and を marks the thing being used.

So:

• 階段を使う = to use the stairs
• エレベーターを使う = to use the elevator

This matches English pretty closely.

You may have also seen sentences like:

• 階段で行きました = I went by the stairs / I went using the stairs

That is also possible, but it uses a different structure:

• 階段を使いました focuses on using the stairs
• 階段で行きました focuses on going by means of the stairs

Japanese often leaves out subjects when they are obvious from context.

Here, 使いました means used, and the listener can naturally understand that the speaker is talking about themselves:

• (私は) 階段を使いました。

Since the meaning is clear, 私は is omitted.

This is extremely common in Japanese. Subjects and objects are often dropped if they are understood from context.

By itself, it usually sounds like the elevator at the station or one specific station elevator relevant to the situation.

Japanese nouns do not normally show singular/plural the way English does. So context decides.

Depending on context, it could refer to:

• one particular elevator
• the station’s elevator in general
• the elevator that the speaker intended to use

If you needed to be very explicit about multiple elevators, Japanese would usually add something else to make that clear.

No, it is not strictly necessary, but it is very common and helpful.

• 駅のエレベーターが故障したので階段を使いました。
• 駅のエレベーターが故障したので、階段を使いました。

Both are correct.

The comma makes the sentence easier to read by showing the break between:

• the reason: 駅のエレベーターが故障したので
• the result/action: 階段を使いました

In written Japanese, commas are often used for clarity and rhythm, not only by strict grammatical rule.

In context, yes, the overall meaning may be understood as the elevator was out of order, even though the literal grammar is broke down.

Japanese often uses a past event like 故障した to explain the reason for a later action:

• It broke down, so I used the stairs

In natural English, that may be translated as:

• The elevator was out of order, so I used the stairs
• Because the station elevator wasn’t working, I used the stairs

So the exact English wording can vary, even though the Japanese structure is based on it broke down.