A termination resistance adjusting circuit includes a first termination resistor circuit, a second termination resistor circuit connected in parallel with the first termination resistor circuit, a resistor circuit for adjustment that adjusts resistances of the first and second termination resistor circuits, a first amplifier circuit that receives a first voltage determined by the resistor circuit for adjustment and a second voltage determined by a reference resistor connected externally, equalizes the first and second voltages, and outputs a resistance adjusting signal to the first and second termination resistor circuits, first and second terminals connected to the first and second termination resistor circuits respectively, and a second amplifier circuit that receives a voltage based on a common voltage of a differential signal supplied to the first and second terminals, and the first or second voltage, and equalizes the voltage based on the common voltage and the first or second voltage.