To provide an electronic device system equipped with an electronic device capable of mounting different sizes of mobile electronic devices.

The electronic device system includes on-board equipment 100 having an attaching/detaching section 170 capable of attaching and detaching a first size portable equipment 10, and an attachment 300 fitted between a second size portable equipment 10 and the on-board equipment 100 in the attaching/detaching section 170 when the second size portable equipment 10 smaller than the first size is mounted on the attaching/detaching section 170.