Provided is an illuminating device that is capable of improving use efficiency of cooling fluid used for cooling LEDs. An illuminating device (4) includes LEDs (13), a chassis (14) including a holding surface (14b) on which the LEDs are arranged in a matrix, cooling members (20) that are disposed on the chassis at positions associated with positions of the LEDs, each of the members including a channel (20a) inside, through which cooling fluid runs and a valve (21) opening and closing the channel, a radiator (22) performing heat exchange between the fluid and air, a pump (24) connected to the members and the radiator by pipes (25, 26) and circulating the fluid, an LED control unit (43) controlling driving of the LEDs, and cooling-member control units (44) controlling driving of the valves of the members associated with the LEDs based on the driving of the LEDs.