HYBRID CONSTRUCTION MACHINE

Provided is a hybrid construction machine that enables to efficiently cool a generator motor, while suppressing an increase in the entire length of a power unit. A motor housing (13) is provided with a bulging portion (21) which is configured to axially bulge from the inner periphery of a motor side connection surface (16a) toward an engine (1) over the entire circumference thereof around an axis, and to engage with the inside of an engine housing (12); and a coolant passage (22) which is configured to flow a coolant for cooling a stator (31) therethrough. The inner peripheral surface of the motor housing (13) including the inner peripheral surface of the bulging portion (21) is configured to come into plane contact with the outer peripheral surface of the stator (31). The coolant passage (22) is disposed at a position axially displaced from the motor side connection surface (16a).