An object of the present invention is to provide a small-sized microwave surgical instrument that improves the convenience of surgical work. The microwave surgical instrument 1 of the present invention includes a surgical instrument main body 21 having an electrode section 24 for emitting a microwave to a biological tissue； a microwave oscillator 51, internally provided in the surgical instrument main body 21, for oscillating a microwave； and an amplifier 52, internally provided in the surgical instrument main body 21 by being connected between the electrode section 24 and the microwave oscillator 51, for amplifying a microwave from the microwave oscillator 51 and transmitting the microwave to the electrode section 24.
