A power unit in a saddle-ride type vehicle in which an arrangement space of an engine constituent part is ensured in an upper space of an engine body. In the power unit, an engine body having a crankshaft and a transmission casing accommodating therein a V-belt type transmission are joined. An oil reservoir portion is formed on a bottom of the engine body to project downward from a lower edge of the transmission casing, and a starter motor is arranged adjacent to a rear wall of the oil reservoir portion.