To provide an electrosurgical power supply apparatus mounted on an electrosurgical instrument and removing or reducing the mixing of noise without lowering a response speed.

This electrosurgical power supply apparatus is provided for an electrosurgical instrument, an output voltage instructing signal is inputted in a signal input portion of a control circuit 13 via a normal mode noise/common mode noise removing circuit 16, drives a switching element provided in a primary side of an insulated transformer 42 of a DC-DC converter circuit 12 via an error amplifier 45 and a PWM control circuit 46 along with an output voltage FB signal formed by dividing a power supply output, and transmits the power to a secondary side. A pulsating flow rectified by a diode bridge 43 is smoothed by an output smoothing filter 14, whose cutoff frequency is heightened, to secure the high speed response and a DC power output is supplied to a high frequency generating circuit. The ground of a power supply output is connected to a frame ground via a condenser 15 to reduce the noise.