Machine, reduction gear for industrial robot and industrial robot configured to detect deterioration of lubricant

The machine configured to detect deterioration of lubricant includes a cleaning member which is configured to clean a lubricant deterioration sensor. A machine body includes a sensor side portion at which the lubricant deterioration sensor is mounted and a cleaning member side portion which is movable with respect to the sensor side portion and at which the cleaning member is mounted. The lubricant deterioration sensor includes a light emitting element, a color light reception element, and a gap forming member having gap forming surfaces at which an oil gap configured to enter the lubricant therein is formed. The gap forming member transmits light emitted from the light emitting element. The oil gap is disposed on an optical path from the light emitting element to the color light reception element. The cleaning member is disposed at a position contacting with the gap forming surfaces when the sensor side portion and the cleaning member side portion move relatively.