An operational amplifier includes a first differential stage, a second differential stage, a second cascade amplifier stage, an output unit, a first switching control unit and a second switching control unit. When an external signal for stopping operation is input, the first switching control unit shuts off a connection between a non-inverting input terminal and a control electrode of one input transistor at each first and second differential stage, and shuts off a connection between an inverting input terminal and a control electrode of another input transistor at the first and second differential stages, and the second switching control unit connects the negative-side power supply voltage terminal to each control gate of the input transistors at the first and second differential stages and to the substrate gates of the input transistors at the first differential stage.