A supercooling apparatus of a simultaneous cooling and heating type multiple air conditioner comprises a liquid pipe header (25) connected to an outdoor heat exchanger (2), a plurality of branch liquid pipes (22a, 22b, 22c) branched from the liquid pipe header (25) and connected to a plurality of indoor heat exchangers (50a, 50b, 50c), respectively, and a supercooling mechanism (60) mounted at at least one of the branch liquid pipes (22a, 22b, 22c) for cooling refrigerant flowing to the indoor heat exchangers (50a, 50b, 50c). The liquid refrigerant discharged from the heating-side indoor heat exchangers (50a, 50b, 50c) is supercooled by supercooling heat exchangers (71a, 71b, 71c), and is then introduced into the cooling-side indoor heat exchangers (50a, 50b; 50c). Consequently, noise generated from the cooling-side heat exchangers during the simultaneous cooling and heating operation is reduced, and cooling capacity of the multi air conditioner is improved.