A reset signal generating circuit outputs a reset signal having a sufficient pulse width even when the power supply voltage is fluctuated. A node B reaches a high level during a power-on reset and is at a low level during operation. When a power supply (Vcc) fluctuates during operation and as soon as a node C reaches a high level, a switch element MN50 turns on, the node B is decreased to a low level, and a stable low-level reset signal RST1 is outputted. When the node B reaches a low level, a switch element MN51 turns off with a delay and capacitors 104 and 105 are gradually charged by a charging circuit 112. When the potential at the node B exceeds a threshold level of an inverter circuit 106, the reset signal RST1 is brought back to a high level, the reset is cancelled, the switch element MN50 is turned off, and the switch element MN51 is brought to be in an on-state again (FIG. 1).