An adjusting apparatus comprises a base, and a supporting frame, a fixed plate, a sliding stand, and a carrier, which are sequential stacked on the base. An optical engine is fixed on the carrier. By rotating the adjusting device, the axis position of optical engine can be adjusted along sliding slots guided by bulges. By using arc surfaces of the sliding stand and the carrier, the adjusting apparatus clips and pushes the blocks of the carrier to adjust the left and right angle of inclination of optical engine. Therefore, the light beam provided by optical engine could project on a screen precisely and reach the optimum projection performance.