According to one embodiment, a constant voltage circuit includes: a first gain stage configured to output a first voltage amplified based on an output voltage and a reference voltage; a first transistor configured to control the output voltage based on the first voltage applied to a gate; and a second circuit configured to control a first signal based on a second voltage obtained by delaying an output timing of the output voltage and a third voltage that is based on the output voltage. In a case of the first signal being at a first logic level, a first current flows through the first gain stage, and in a case of the first signal being at a second logic level, a second current flows through the first gain stage.