A laser light deflection amount detecting apparatus detects an amount of deflection of laser light and includes a laser light source, a first polarizing beam splitter that splits the laser light emitted by the laser light source, an optical system that rotates at least one of linearly polarized components around an optical axis orthogonally and that acquires a combined light of the linearly polarized components at least one of which is rotated, a light blocking member, a second polarizing beam splitter, and two light receiving elements that measure an amount of light of the polarized components resulting from the splitting by the second polarizing beam splitter.