PROBLEM TO BE SOLVED: To provide a hybrid riding type lawn mower securely reducible of fuel cost without requiring complicated operation while securing stable lawn-mowing traveling by avoiding deterioration in emission, noise and fuel efficiency caused by excessive loads in the lawn-mowing traveling.SOLUTION: The hybrid riding type lawn mower includes: an internal combustion motor (3) for feeding power to traveling and lawn mowing working devices, and a secondary battery (4) for accumulating the electric power converted by the power of the motor, which are disposed in a machine body configured to mow grass while traveling in a sod. The hybrid riding type lawn mower is configured to operate the working devices with the electric power fed from the secondary battery (4). The internal combustion motor (3) includes a control part (C) for controlling the rotation by switching two control modes: a working mode and a charging mode. In the working mode, the lawn mower is operated with rated output； and in the charging mode, the lawn mower is operated in the minimum fuel cost range for charging the secondary battery (4). These two control modes are switched according to the operating situation of the working devices.【課題】芝刈り走行における過大負荷に伴う排ガス、騒音、燃費の悪化等を回避して安定した芝刈り走行を確保しつつ、煩雑な操作を要することなく、確実な低燃費化を可能とするハイブリッド式乗用芝刈り機を提供する。【解決手段】ハイブリッド式乗用芝刈り機は、草地走行しつつ芝刈り可能に構成した機体に、走行および芝刈りの作業機器に動力を供給する内燃式原動機（３）と、その動力による変換電力を蓄電する二次電池（４）と、この二次電池（４）の電力供給によって作業機器を動作可能に構成され、上記内燃式原動機（３）は、作業モードと充電モードの２つの制御モードを切替えて回転制御する制御部（Ｃ）を備え、作業モードは定格出力で運転し、充電モードは二次電池（４）の充電を行うための最小燃費範囲で運転し、これら２つの制御モードを作業機器の動作状況に応じて切替えるものである。【選択図】図４
