The present invention provides a higher-performance assist device which is safer by using a wireless charging technique. The assist device includes a detecting portion and an assist device driving portion. The detecting portion includes a sensor, a first transmitting/receiving circuit, a first data processing circuit, a first charging circuit, and a first battery. The assist device driving portion includes a driving portion, a second data processing circuit, a second transmitting/receiving circuit, a second charging circuit, and a second battery. Electromagnetic waves are transmitted from the second transmitting/receiving circuit provided in the assist device driving portion, and the first transmitting/receiving circuit provided in the detecting portion receives the electromagnetic waves. Induced electromotive force generated at this time is input to the first charging circuit through the first data processing circuit provided in the detecting portion, and the first battery provided in the detecting portion is charged.
