Thank you all.
Oh, now I see that the main difference of these words are the region.
In Korea, I learned the words of toilet facilities as a restroom, bathroom and rarely Roo(I heard this word is using in the UK.) in English class. But in a public place, they are written "toilet".
When I went to Japan, they use the "toilet".
In Canada, I heard "wash room" a lot either.
Okay, I will use "restroom" when I go to the America someday.:)
p.s. when you travel in Korea and if you don't know how to say it in Korean, I suggest you ask to Korean people "restroom" first and then "bathroom", "toilet".