Confused about two way wiring on stair case
That's a 4 way switch, not a 3 way switch (your replacement device is a 3 way). That switch is in the middle of the chain, and you need to replace it with another 4 way switch. 

I found a tutorial on 4 way wiring here: http://www.wfu.edu/~matthews/courses/p230/switches/SwitchesTut.html