An impedance adjusting circuit that includes an external terminal to which an external resistor is connected, a first transistor array of a first conductivity type that is connected in parallel between the external terminal and a first power supply terminal and changes a voltage of the external terminal by adjusting an impedance in response to a first control signal, a second transistor array of a second conductivity type that is connected in parallel between the external terminal and a second power supply terminal and changes the voltage of the external terminal by adjusting the impedance in response to a second control signal, and a control circuit that specifies the first control signal according to a comparison result between the voltage of the external terminal and a reference voltage and specifies the second control signal in a different period from a period to specify the first control signal.