A ceiling-embedded air conditioner allowing good balance of air passing through heat exchangers is provided through optimization of configuration and a mounting position of an electronic part box. The ceiling-embedded air conditioner is in a casing main body (2) having a quadrangle shape and provided with first to fourth side plates (22a-22d), and comprises a heat exchanger (6) having a quadrangle shape and provided with first to fourth heat exchanger units (6a-6d). A corner (A) used for pipe connection is provided with ends (63, 64) of the heat exchanger (6). The electronic part box (9) is configured to an L shape by adopting the corner (A) as a starting point.