A microwave plasma source for generating a microwave plasma inside a chamber by radiating a microwave into the chamber, includes: a microwave oscillator for oscillating the microwave and vary an oscillation frequency thereof; a waveguide through which the microwave propagates; an antenna part including a slot antenna for radiating the microwave into the chamber and having a predetermined pattern of slots, and a microwave-transmitting plate constituting a ceiling plate of the chamber and made of a dielectric material through which the microwave radiated from the slots transmits; temperature detectors for detecting temperatures at plural positions of the antenna part outside the chamber when the microwave plasma is generated; and a frequency controller for receiving detection signals obtained by the temperature detectors and controlling the oscillation frequency of the microwave oscillator so that a plasma density distribution inside the chamber becomes a desired distribution based on the detection signals.