The present invention relates to an improved heat radiating device for lamp, comprising an exhaust space configured around the periphery of lamp stand, an exhaust fan disposed at the top of exhaust space, and simultaneously a radiator and a plurality of heat conductors at the back of the printed circuit board of a light emitting diode (LED) lamp set where the heat conductors extend to the peripheral inner wall of lamp stand in the exhaust space. Through such a radiating device, high heat generated by the LED lamp set can be dissipated through the radiator and through the plurality of heat conductors to the periphery of lamp stand in the exhaust space, thereby enlarging the heat dissipation area. In addition, through the exhaust fan disposed at the top of the exhaust space, ventilation can take place continuously to let the heat in the exhaust space be vented rapidly, thereby achieving fast heat dissipation and prolonging the service life of LED lamp.