An illuminating device comprises a first light source in which LED chips are arranged in an array shape and a second light source in which LED chips are arranged in an array shape. The two light sources of each illuminating device are arranged such that the main light-emission optical axes of the light sources are perpendicular to each other. Moreover, a time-division switching mirror is provided at a crossing position between the main light-emission optical axes. The first light source and the second light source alternately emit pulses of light. The pulsed emission is a method of supplying a large amount of electric currents to the LED chips in a short time period, and a light-emitting amount increases compared to a steady-state emission of the LED chips. The time-division switching mirror becomes a transmitting state when the first light source is lighted, and becomes a reflecting state when the second light source is lighted.