PURPOSE: To reduce manufacturing man-hours and reduce the cost by concurrently generating many resonance chambers each constituted of a guide passage opened on one face of a soft porous foam body and a hollow section formed at the depth of the guide passage and having a cross sectional area larger than that of the guide passage.

CONSTITUTION: A urethane foam material is injected into the cavity of a molding die to mold a urethane foam body having many resonance chambers 1 each constituted of a guide passage 11 opened on one face and a hollow section 12 having a cross sectional area larger than that of the guide passage 11 at the depth. This urethane foam body is fitted to the wall face of the engine room of a vehicle so that the opening faces of the guide passages 11 are faced to the engine. The noises generated from the engine are absorbed by this sound absorbing member itself, the noises entering into the resonance chambers 1 from the guide passages 11 are resonated and absorbed in the resonance chambers 1 tuned to the prescribed frequency. The porous foam body having many resonance chambers 1 can be simply manufactured in one molding process.