Transmission unit and power system

A clutch unit () includes a coupling element () configured to, in a power transmission enabled manner, couple an output shaft () of an engine () and an input shaft () of a hydraulic pump () driven by driving force of the engine (), and a motor generator () configured to generate driving force separately from the engine (), in which the coupling element () includes a driving-side coupling portion () configured to be coupled to a first coupling portion () that is provided in the output shaft (), and a driven-side coupling portion () configured to be coupled to a second coupling portion () that is provided in the input shaft () and that is configured to be coupled to the first coupling portion ().