To provide an on-vehicle device that can be made thin and can ensure high operability of an IC card used therefor, and structure for mounting the on-vehicle device.

An on-ETC vehicle device 1 is a box-shaped device into which an ETC card 3 as an IC card is removably loaded, and the on-ETC vehicle device 1 is adhered to a surface of a wall 7 of a vehicle (mount surface 9) by a double-sided adhesive tape 5. In particular, an internal substrate 13 (therefore a card connector 15) is inclined at a predetermined angle to a vehicle sidewall part 17 of the on-ETC vehicle device 1. Namely, the internal substrate 13 and the card connector 15 are inclined so that the distance to the vehicle sidewall part 17 becomes longer at the side of an insertion sidewall part 23 than at the side of a bottom sidewall part 25. Thus, a moving path of the ETC card 3 to be put in and put out of the card connector 15 is set to also be inclined at the above angle to the vehicle sidewall part 17.