A hybrid construction machine according to the present invention is constructed to drive electric motors (6, 7, 13, 15, 23, 25) by means of power of a power generator (11) to be driven by an engine (10), power of an auxiliary battery (42) and power of a main battery (12) charged with power of the power generator (11). The hybrid construction machine has a switch (43) for switching to drive the electric motors (6, 7, 13, 15, 23, 25) by means of power of at least one of the power generator (11) and the main battery (12) when operating normally and to drive the electric motors (6, 7, 13, 15, 23, 25) by means of power of the auxiliary battery (42) when operating emergency such that the electric motors (6, 7, 13, 15, 23, 25) can not be driven by means of the normal power.