A fuel gauge circuit detects a residual quantity of a battery 1 and is disposed on a substrate 20 together with a protection circuit 40 which protects chargingdischarging of the battery 1. The electrodes produce an environment containing charged toner particles to assist in electrostatic printing. The silica layer formed on the surface of the molded polymer assists in formation of a proper bond. With the rapid change in the magnetization flux over time, in the conductive attenuation body, an eddy current is generated in a direction canceling the magnetization flux and thus the magnetization field weakens.