An ellipsometer for aligning incident angle comprising: a main frame shaping half circle and flat surface on which a plurality of grooves are radial and circumferential directionally carved; a specimen stage, which is installed at the groove-caved surface of the main frame, for tilting a specimen on a upper surface of the specimen stage with respect to horizontal direction and translating the specimen upward and downward; a polarizing unit, which is capable of fixing and moving on the groove-carved surface of the main frame, for polarizing a light from a light source and outputting the polarized light to the specimen, and moving on the groove-carved surface; and a light detecting unit, which is capable of fixing and moving on the groove-carved surface, for a reflection light from the specimen.