To provide an inexpensive electronic toll collection system on-vehicle device capable of reducing the number of necessary springs (elastic members) though an ejection button is a push-type.

In the electronic toll collection system on-vehicle device, a transmission member 33 connecting the ejection button 3 and a locking member 32 is formed as a member in which moving back and forth motions of the ejection button 3 are transmitted to the locking member 32 while the motions are converted into turning motions in the forward and reverse direction between a connecting position EP where a slide member side connection section 31b and locking member side connection section 32e are connected with each other and a connection releasing position RP for releasing the connection of both sections 31b and 32e. The locking member 32 can be turned by operating together with the moving back and forth motions of the ejection button 3 without having the elastic member which makes the locking member 32 move to the connecting position EP with a slide member 31, and an attaching and detaching operation of a card EC can be secured.