To provide a method and apparatus for performing high-performance defrosting in a short time in which the outflow a drip from a frozen object is prevented, the oxidation of a frozen object is reduced and the temperature difference between the surface part and the inside of a frozen object is reduced regardless of the shape and temperature of the frozen object.

When defrosting a frozen object by microwave heating under reduced pressure in a vessel, the following processes are repeated: stopping the microwave heating by a microwave discharge generated from a charge generator in the decompression vessel before the arrival of a situation that a drip-like liquid flows out from the frozen object 12 in a state of warm-up in a process of microwave heating while advancing decompression; advancing still more decompression in that state down to the decompression degree where sublimation can occur from the frozen object 12; then returning to a defined decompression degree where microwave heating can be resumed; performing microwave heating in an adequate output power while advancing decompression again and; stopping the microwave heating again by a microwave discharge generated from a charge generator before the arrival of a situation that a drip-like liquid flows out from the frozen object 12 in a state of warm-up.