PURPOSE: To provide the output buffer circuit which makes a power source generate no noise while securing sufficient load driving ability.

CONSTITUTION: A P channel MOS transistor(TR) 1 and an N channel MOS TR2 are connected in series between a high-potential side power source Vcc and a low-potential side power source GND, and an input signal IN is inputted to the gates of both the TRs 1 and 2. Output signals OUT are outputted from the drains of both the TRs 1 and 2. A subordinate buffer circuit 2 which operates when the output signal OUT exceeds a previously set threshold value to increase the amplitude of the output signal OUT is connected to the main buffer circuit 1 composed of the TRs 1 and 2.