In a voltage detecting circuit, a transistor is configured as a P-type MOSFET, and includes a source connected with an input terminal, a gate connected with a ground voltage terminal and a drain connected with an output terminal. A transistor is configured as a P-type MOSFET, and includes a gate and a source connected with the output terminal and a drain connected with the ground terminal. Gate width and gate length of the transistor and gate width and gate length of the transistor are adjusted so that source-drain current flowing between the source and the drain of the transistor becomes equal to source-drain current flowing between the source and the drain of the transistor when the voltage applied to the input terminal is set to be preset trigger voltage. This configuration accomplishes detecting that the input voltage exceeds the trigger voltage with simple configuration.