A power supply apparatus for operation for outputting power to a surgical instrument includes a temperature detection section for detecting a temperature of the surgical instrument, and an abnormality detection section for detecting an abnormality of the surgical instrument on the basis of the detected temperature. The temperature detection section detects the temperature by measuring the electric capacitance of the surgical instrument or directly measures the temperature of the surgical instrument by using a temperature measurement device. More specifically, the abnormality detection section detects the abnormality according to whether or not a temperature variation amount of the surgical instrument per unit time exceeds a predetermined threshold. Further, when the abnormality detection section detects an abnormality, the abnormality detection section stops the output of the power to the surgical instrument. By detecting an abnormality in the manner described above, the surgical instrument can be prevented from being broken.