There is to provide a communication device capable of reducing the power consumption. The communication device includes a battery and a transmission circuit for transmitting a signal of a desired transmission frequency upon receipt of a power supply from the battery. The transmission circuit includes a first oscillator for oscillating a signal, an amplifier for amplifying the signal oscillated by the first oscillator, and a filter circuit for eliminating a harmonic component included in the signal output from the amplifier. The filter circuit includes an extracting unit for extracting a frequency signal of n (n≧2) times frequencies of the transmission frequency from the signal output from the amplifier and a recovery unit for recovering the battery with DC component of the extracted n times frequency signal.