A controller controls a bi-directional converter which includes: a first input/output terminal and a second input/output terminal for receiving and outputting a voltage stepped up by a step-up operation and a voltage stepped down by a step-down operation; a first switching element; a second switching element; and an inductor. The controller includes: a first driver which controls the first switching element via a first resistance circuit; a second driver which controls the second switching element via a second resistance circuit; and an operation mode setter which selects one of the step-up operation and the step-down operation, wherein at least one of the first resistance circuit and the second resistance circuit is a variable resistance circuit which has a resistance value that varies for the step-up operation and the step-down operation, in accordance with selection made by the operation mode setter.