This patent specification describes a boost circuit which includes an inductor wired to an input terminal, a switching device connected between the inductor and a ground, a rectifying device formed of a MOS transistor and connected between the inductor and an output terminal and configured to be switched in accordance with the control signal, a first transistor wired to the input terminal and to a substrate gate of the rectifying device, a second transistor wired to the substrate gate of the rectifying device and to the output terminal and a controller configured to control each operation of the switching device, the rectifying device and the first and second transistors so that the first transistor is off and the second transistor is on in a boost mode and the first transistor is on and the second transistor is off in a boost suspend mode.