An optical reading device of a scanning apparatus includes a housing, two movable mirror clamps and two supporting plates. The housing contains therein a light source, a mirror set, a lens and an image sensor. These two movable mirror clamps are used for clamping both edges of a specific reflective mirror of said mirror set such that the position of said specific reflective mirror is adjustable by an assembler. These two supporting plates are protruded from opposite sides of said housing for supporting said movable mirror clamps.