To provide a voltage regulator which is capable of testing a phase compensation capacitor without impairing stability as a regulator and prevents a chip area from being increased. A voltage regulator is configured to be equipped with a phase compensation capacitance test circuit for a phase compensation circuit and a negative voltage detection circuit for an external output voltage adjustment terminal and to apply a negative voltage to the external output voltage adjustment terminal to thereby start up the phase compensation capacitance test circuit, and measure the discharge time or current of a phase compensation capacitor to thereby test whether the phase compensation capacitor is good or not.