In a method of determining a deterioration state of an object, the deterioration state of the object is determined by determining whether a calculated value reaches a state determination threshold value or not, the calculated value utilizing at least one of brightness and a color component value calculated from a detection value detected by an optical sensor. The optical sensor includes an examination section containing liquid, a light emitting element emitting detection light toward the examination section, and a light receiving element detecting color information of the detection light traveled through the liquid.