PURPOSE: To obtain a relatively large silencing effect by providing a cylindrical part opened toward the downstream of an air flow path in a core silencing part, to form a large sound absorbing surface against a noise emitted from a mixed flow fan.

CONSTITUTION: A core silencing part 14 is provided with a core inner cylinder 8 opened toward the downstream of an air flow path, core peripheral sound absorbing material 15 of covering the peripheral surface of the core inner cylinder 8 and a core internal peripheral sound absorbing material 15a of covering the internal peripheral surface to form a silencing in-core space 9, to fix the core silencing part to a fan outer cylinder 9 by a suspending fixture 10. A shape of the core inner cylinder 8 is formed so as to enlarge a sound receiving surface in the downstream into a diameter of relation where S1 (diameter in the downstream) > S2 (diameter in the upstream). When the relation S1/S2 is set to 1.6 to 1.2, in a condition of small ventilating resistance, a silencing effect can be increased. Most of noise caused in a mixed flow fan is absorbed by the core internal peripheral sound absorbing material 15a, to disappear. Partly a noise propagated to detour the core silencing part 14 is absorbed by an outer cylinder sound absorbing material 13 and by the core peripheral sound absorbing material 15, to reduce the amount of noise emitted from a suction port 11.