Heat source unit installed into ceiling and air conditioner

A heat source unit, for facilitating the maintenance of a fan assembly even in a ceiling having a limited space, including: a rectangular housing (12); an air inlet (24) and an air outlet (26) which are provided in the same side surface of the housing; a fan assembly (18) which includes a sirocco fan (28) disposed in the housing and a fan motor (30) driving the sirocco fan; a heat exchanger (16) which performs a heat exchange using air sucked from the air inlet; and a compressor (14). Particularly, on a side surface (36) (rear side surface) opposed to a side surface (22) (front side surface) on which the air inlet of the housing is provided, there is provided an openable extraction port which is used to extract the fan assembly. In addition, on a separation plate (38) of the housing is provided a pair of guide rails (58) which are disposed in a direction along left and right side surfaces (32 and 34) of the housing, and a mounting member (43) to which the fan assembly is fixed is guided by the guide rails so as to be extracted to the outside of the housing in a sliding manner.