To suppress sudden output variation in an engine when controlling an output of the engine in response to a load state of a hybrid construction machine, concerning the hybrid construction machine driving the load using an engine and an energy storage device as a power source.

A device for control of the hybrid construction machine includes: a fuzzy inference unit 42 inferring increase and decrease of an output of the engine 12 on the basis of a fuzzy rule in which at least one of an amount of charge of the energy storage device 34, variation in increase and decrease of the amount of charge of the energy storage device 34, consumption power of a load, and variation in increase and decrease of the consumption power of the load is an antecedent part and the output of the engine 12 is a consequent part. The output of the engine 12 is controlled on the basis of the inference result of the fuzzy inference unit 42.