When you create the func_train entity that makes up the elevator platform, it combines all the selected brushes (in your case it's just one as you've just made a simple platform) as one entity. This entity is placed at the origin of the path_corner entities, and extend in the positive direction of each axis.
Basically, the platform will be placed with the path_corner at its bottom left in all the views. if you zoom in, you'll see a cross in the centre of the path_corner - this is the precise position of the entity's origin.
I've fixed it for you anyway, have a look at this map file if you don't understand.
- Dagless
edit:
I just realised you aren't a natural english speaker, so I've drawn you a diagram to help me explain.
1) shows the brush which you are turning into a func_train to be the platform. The red cross shows the point that it gets placed at the center of the path_corner entity.
2) shows how the path_corners have a little cross in the middle, which is what you want to use to place the path_corners in the right place to align the platform.
You will need to put the path corners diagonally lower and to the left on the top down view. It's easy with your elevator.bsp map because the platform is square and the same size as the 'shaft' that you want it to go up and down in. This means you can just put the path_corner at the bottom left of the shaft (making sure the little cross is perfectly in the bottom left corner) on the top down view.
Hope this helps!
