An assembling method of a vehicular air-conditioning apparatus including various equipment, which is required for air-conditioning a vehicle, mounted in a vehicular-air-conditioner frame on a production line includes modularization of, among the various equipment, at least a compressor, an indoor heat exchanger, and an outdoor heat exchanger off the production line, and, further, modularization of a refrigeration cycle by connecting the above modules with refrigerant pipes off the production line, as well as incorporating the modularized refrigerant cycle into assembly work on the production line as a refrigerant cycle module.