A construction machine comprises an electric motor/generator coupled to an electricity accumulator, an engine, a transmission coupled to drive wheels, an epicyclic gearing for coupling an output shaft of the electric motor/generator, an output shaft of the engine, and an input shaft of the transmission, the engine torque and/or the generator torque being transmitted to drive wheels, a clutch for directly coupling two among the output shaft of the electric motor/generator, the output shaft of the engine, and the input shaft of the transmission, and a controller configured to, under a condition in which the clutch is in an off-state, control engine speed based on the degree to which the accelerator is open and on the amount of electricity in the electricity accumulator, to control shifting of the transmission gear position based on the accelerator opening degree, operational state of the generator, and the electricity amount.