PURPOSE: To provide a high performance active muffling device employing an inexpensive computation device by controlling the noise and interference waves which cancel the noise so that they synchronize with inverse amplitudes at a sound interference position.

CONSTITUTION: First, a press is stopped, multiplying coefficient data H set in a coefficient control section 14 is multiplied with the noise data stored in a noise data memory 13 by using a multiplyer 15, interference wave data equivalent to a single operation are supplied to a D/A converter 16, converted into analog signals and interference sound waves are generated through a filter, an amplifier and an interference sound output speaker. Next, the press is started, noise is generated and a control section 3 multiplies the noise data of the memory 13 with multiplying coefficients H in the multiplier 16 by using the synchronization pulse input from a noise synchronization means and interference sound waves are outputted from the speaker. A delay control section 18 controls the start of the noise data of the memory 13 and adjusts the timing of interference sound wave generation.