A resistance adjusting circuit including, a reference resistor, a first power source configured to output a first voltage, a first current source configured to output a first current based on a reference current set by using the reference resistor, a first variable resistor, a second current source configured to output a second current obtained by multiplying the first current by a reciprocal ratio, the reciprocal ratio being obtained as a reciprocal number of a ratio of a target resistance of the first variable resistor to a resistance of the reference resistor, and a controller configured to set a resistance of the first variable resistor so that a voltage at a second terminal of the reference resistor and a voltage at a connecting part of the first variable resistor and the second current source become equal to each other.