A street illuminating device includes a retaining frame, a light source module, and a heat dissipating module. The light source module includes a printed circuit board retained in the retaining frame, a number of solid state lighting elements, and a light reflecting plate. The printed circuit board has a first surface and an opposite second surface. The solid state lighting elements are arranged on the first surface of the printed circuit board. The light reflecting plate includes a number of through holes with inner reflecting surfaces. The light reflecting plate is disposed on the first surface of the printed circuit board with the solid state lighting elements received in the respective through holes. The heat dissipating module is in thermal contact with the second surface of the printed circuit board.