A walk-behind working machine includes a first clutch mechanism for connecting or disconnecting drive between an engine and a working member of the working machine. The first clutch mechanism includes a first clutch lever having a first activating member. A second clutch mechanism is configured to connect or disconnect drive between the engine and traveling members of the working machine. The second clutch mechanism includes a second clutch lever having a second activating member. A throttle regulating mechanism has a pivoting member for engagement with one of the first activating member of the first clutch mechanism and the second activating member of the second clutch mechanism so as to undergo pivotal movement to shift a throttle for the engine from a first opened position in which an idling engine speed is produced to a second opened position in which a working-machine-activating engine speed is produced.