Sharp fluctuations of an internal voltage when an internal voltage generating circuit is activated or inactivated are prevented. The internal voltage generating circuit to supply the internal voltage generated from an external voltage to an internal power supply line, a control circuit to control an operation of the internal voltage generating circuit, and a voltage detection circuit to detect a level of a first voltage are included. When, for example, the internal voltage generating circuit is activated, the control circuit stepwise increases supply ability of the internal voltage at a first speed and when the internal voltage generating circuit is inactivated, the control circuit stepwise reduces the supply ability of the internal voltage at a second speed that is different from the first speed. Accordingly, wild fluctuations of the internal voltage when the internal voltage generating circuit is activated/inactivated can optimally be prevented for each case.