To provide the washing apparatus of an air filter unit, which can be made compact and whose space can be saved, whose construction is simple and installation work is easy, and by which work efficiency and treatment efficiency can be improved.

This washing apparatus of an air filter unit is provided with: a plurality of handling devices 38 disposed along a circulation route with equal intervals and detachably holding the air filter unit; a conveying device 30 simultaneously moving all the handling devices along the circulation route while keeping the intervals of the handling devices; and a plurality of treatment tanks 22, 24, 26, 28 disposed along the circulation route with equal intervals in the order of washing processes of the air filter unit. The handling devices 38 move through the treatment tanks 22, 24, 26, 28 in this order, and the air filter unit held by the handling devices 38 is treated in the treatment tanks 22, 24, 26, 28 in this order.