A portable working machine includes a gaseous-fueled engine, a working unit driven by the engine, a control unit for controlling the engine and the working unit, and an acceleration sensor capable of detecting accelerations in two mutually perpendicular horizontal directions relative to a vertical line, which is induced in the portable working machine. The control unit is configured to determine a tip angle of the portable working machine based on the horizontal accelerations detected by the acceleration sensor and issue a stop instruction to the engine when it determines that the tip angle exceeds a preset reference angle.