PURPOSE: To stop constant voltage power supply output at a reset signal output, by making the reference voltage for a constant voltage power supply circuit and a reset circuit common so that the operation limit voltage of a control logical circuit and a reset detection voltage can be equal.

CONSTITUTION: A Zener diode 19 is set as a reference voltage element, and a current flows with fixed resistors 17, 18. A transistor (TR) 15 detects a current flowing to the Zener diode 19 and collector current is outputted. For example, if a power supply voltage Vcc is decreased and approaches the reference voltage, the current decreases extermely and the TR15 turns off. A fixed resistor 16 is ready to obtain logical outputs "0", "1" and the logic "0" is obtained at the on- state of TR15 and a reset signal is generated via a diode 13. Thus, the function of a control logical circuit 24 is stopped. At reset, a voltage of the resistor 16 is at "0", the base voltage of a TR20 approaches "0" via a diode 23 to turn off the TR20 and to stop the output of constant voltage power supply.