PURPOSE: To suppress the temperature rise of a magnetic circuit part as much as possible by coupling one terminal part of a heat pipe with the magnetic circuit part and then by protruding the other terminal part at the front face side of a diaphragm through a coil bobbin.

CONSTITUTION: Heating part 25a of heat pipe 25 is inserted into and fixed in pole piece 13 of magntic circuit part 12 of speaker unit 11 and radiation part 25b is protruded to the surface side of diaphragm 19 by penetrating coil bobbin 17 through radiator 28. As a result, heat generated at circuit part 12 is radiated to the front face side of diaphragm 19 in the cycle of evaporation and liquefaction of a working liquid sealed in pipe 25 at a low pressure through heating part 25a and radiation part 25b, but since air alows into bobbin 17 by reciprocating through the vibration of diaphragm 19, radiation part 25b of pipe 25 is forcibly cooled by the air to alternate the evaporation and liquefaction of the working liquid at a high speed. Thus, the temperature rise of circuit part 12 is suppressed, so that audio pnput signals to coil 16 can greatly be increased.