A voltage converter performs a step-up operation and step-down operation in parallel. The step-up operation raises an input voltage to a voltage that is N (N≥1) times the input voltage. The step-down operation lowers the input voltage to a voltage that is M (0≤M≤1) times the input voltage. The voltage converter outputs the voltage transformed through the step-up operation and the step-down operation from output terminals. A current detection circuit detects an output current. A step-up adjustment circuit decreases N if the output current is higher than a reference current, and increases N if the output current is lower than the reference current. A step-down adjustment circuit decreases M if the output current is higher than a reference current, and increases M if the output current is lower than the reference current. The reference current is higher than the reference current.