A method of determining a deterioration state of an object, comprising: determining a deterioration state of the object by determining whether a calculated value reaches a state determination threshold value or not, the calculated value utilizing a color component value calculated from detection values detected by a color sensor of an optical sensor, wherein the detection value includes an R value, a G value, and a B value, wherein the optical sensor includes an examination section containing liquid, a light emitting element emitting detection light toward the examination section, and the color sensor detecting the detection values as color information of the detection light traveled through the liquid, wherein the object is the liquid, and the state determination threshold value is a liquid deterioration determination threshold value to determine whether the liquid is deteriorated or not, or wherein the object is a machine using the liquid, and the state determination threshold value is a failure determination threshold value to determine whether the machine is broken or not, wherein the calculated value includes a maximum color difference between a maximum color component value and a minimum color component value, the maximum color difference increasing as the operating time increases and then decreasing upon reaching an extreme value, and when it is determined that the calculated maximum color difference reached the extreme value and is less than or equal to the state determination threshold value, it is determined that the object is in a deteriorated state, wherein the maximum color component value and the minimum color component value each calculated from at least one of the detection value. determining a deterioration state of the object by determining whether a calculated value reaches a state determination threshold value or not, the calculated value utilizing a color component value calculated from detection values detected by a color sensor of an optical sensor, wherein the detection value includes an R value, a G value, and a B value, wherein the optical sensor includes an examination section containing liquid, a light emitting element emitting detection light toward the examination section, and the color sensor detecting the detection values as color information of the detection light traveled through the liquid, wherein the object is the liquid, and the state determination threshold value is a liquid deterioration determination threshold value to determine whether the liquid is deteriorated or not, or wherein the object is a machine using the liquid, and the state determination threshold value is a failure determination threshold value to determine whether the machine is broken or not, wherein the calculated value includes a maximum color difference between a maximum color component value and a minimum color component value, the maximum color difference increasing as the operating time increases and then decreasing upon reaching an extreme value, and when it is determined that the calculated maximum color difference reached the extreme value and is less than or equal to the state determination threshold value, it is determined that the object is in a deteriorated state, wherein the maximum color component value and the minimum color component value each calculated from at least one of the detection value.