PURPOSE: To produce a sintered body of uniform and good quality by detecting the change in the state of a sintering powder part by the use of ultrasonic waves, and suitably changing and controlling pressurizing force, conducting electric power, etc. in accordance with the same.

CONSTITUTION: First, alloy powder 1 is packed in a molding die 2, and while it is lightly pressurized by operating a lower pressurizing punch 3 with a cylinder 5, pressurizing sintering electric power is supplied from an electric power source circuit 11. At the same, an oscillator 14 is operated to emit ultrasonic waves from a transmitter 13. The ultrasonic waves transmitted through a sintering powder part 1 are received in a receiver 15. The alloy powder 1 is deformed and shrank by the heating with the Joule heat of the conducting electric current and the light pressurizing with the punch 3, whereby its density is increased. The output of the ultrasonic wave intensity detected with the receiver 15 is detected with a level detector 17 via an amplifier 16, and when it attains the prescribed value, a controller 10 opens a changeover valve 8 to operate a cylinder 6 which in turn drives an upper punch 4, and also drives a lower punch 3 simultaneously, thereby exerting the final molding high pressure. This completes molding and sintering.