Provided is a voltage regulator capable of controlling an output voltage to a predetermined voltage quickly after an undershoot occurs in the output voltage. The voltage regulator includes: an undershoot detection circuit configured to detect a voltage that is based on an output voltage of the voltage regulator, and output a current corresponding to an undershoot amount of the output voltage; and an I-V converter circuit configured to control a current flowing through an output transistor based on a current controlled by an output of an error amplifier and a current flowing from the undershoot detection circuit.