To provide hybrid construction machinery which can be easily hybridized even if the construction machinery is a rear super-small revolving type or a super-small revolving type.

A compact hybrid excavator of a rear super-small revolving type includes: an engine 11; a hydraulic pump 21 in which an input shaft 21a is coaxially connected to an output shaft 11a of the engine 11; an electric generator/motor 31 in which a rotational shaft 31a is connected to the output shaft 11a of the engine 11 and the input shaft 21a of the hydraulic pump 21 via a gear mechanism 6; and a battery 33 for delivering/receiving electric power to/from the electric generator/motor 31. The electric generator/motor 31 is disposed at a position where the bottom of the electric generator/motor 31 is in the vertically upper side of the shaft center of the input shaft 21a of the hydraulic pump 21, horizontally overlapping with the hydraulic pump 21 in top view.