A saddle type vehicle comprising: an internal combustion engine, the internal combustion engine comprising: a crankcase; a crankshaft, the crankshaft being supported by the crankcase, the crankshaft configured to receive rotary motion on burning of air and fuel mixture within the IC engine; an output shaft, the output shaft being configured to receive rotary motion from the crankshaft, the output shaft being operably connected to provide rotary motion output to a rear wheel of the saddle type vehicle; a first transmission mechanism (411, 412, 421, 413) interposed between the crankshaft and the output shaft, the first transmission mechanism (411, 412, 421, 413) configured to provide variable torque rotary motion output at the output shaft; and an engine sprocket being exposed in a width direction of the vehicle through a clutch cover wherein the clutch cover enclosing a left-hand side of the IC engine in the width direction; an electric motor unit, the electric motor unit being detachably mounted on the external surface of the crankcase of the IC engine, the electric motor unit comprising: an electric motor, the electric motor being operably connected to the output shaft to provide a parallel torque assist at the output shaft along with the IC engine; a second transmission mechanism, the second transmission mechanism being interposed between the electric motor and the output shaft to provide torque multiplication rotary motion output at the output shaft; wherein the electric motor unit comprises a first housing member and a second housing member assembled to form a space to accommodate the electric motor and the second transmission mechanism; and wherein the second housing member of the electric motor unit being configured to attached to the clutch cover. a crankcase; a crankshaft, the crankshaft being supported by the crankcase, the crankshaft configured to receive rotary motion on burning of air and fuel mixture within the IC engine; an output shaft, the output shaft being configured to receive rotary motion from the crankshaft, the output shaft being operably connected to provide rotary motion output to a rear wheel of the saddle type vehicle; a first transmission mechanism (411, 412, 421, 413) interposed between the crankshaft and the output shaft, the first transmission mechanism (411, 412, 421, 413) configured to provide variable torque rotary motion output at the output shaft; and an engine sprocket being exposed in a width direction of the vehicle through a clutch cover wherein the clutch cover enclosing a left-hand side of the IC engine in the width direction; an electric motor, the electric motor being operably connected to the output shaft to provide a parallel torque assist at the output shaft along with the IC engine; a second transmission mechanism, the second transmission mechanism being interposed between the electric motor and the output shaft to provide torque multiplication rotary motion output at the output shaft; wherein the electric motor unit comprises a first housing member and a second housing member assembled to form a space to accommodate the electric motor and the second transmission mechanism; and wherein the second housing member of the electric motor unit being configured to attached to the clutch cover. wherein the electric motor unit comprises a first housing member and a second housing member assembled to form a space to accommodate the electric motor and the second transmission mechanism; and wherein the second housing member of the electric motor unit being configured to attached to the clutch cover.