A power control circuit includes a detection device, a first control device, and a second control device. When the detection signal is changed from lower to higher than the first voltage, the first control device's output is changed to the second potential. When the detection signal is changed from higher to lower than the second voltage, the first control device's output is changed to the first potential. When the detection signal is changed from lower to higher than the third voltage, the second control device's output is changed to the fourth potential. When the detection signal is changed from higher to lower than the fourth voltage, the second control device's output is changed to the third potential. According to the first or second potentials, the circuit device turns on/off the first function. According to the third or fourth potentials, the circuit device turns on/off the second function.