To provide a detergent composition having high safety and excellent cleaning power to the stain of asphalt pitch, wax, etc., applied to an optical part and usable as a substitute for a chlorine-based solvent.

The detergent composition, especially a detergent composition for optical part contains a ≥5C α-olefin oxide and optionally further a terpene and/or a (poly)alkylene glycol lower alkyl ether. The detergent composition exhibits excellent cleaning power to the stain of asphalt pitch, wax, etc., attached to an optical part such as lens and prism in the processing of the part.