This paper describes our attempts to improve the power generation efficiency of single-phase permanent magnet generators of outer-rotor type for motorcycles by their reducing electric losses (iron loss and copper loss) by electromagnetic analysis.In this study, we first broke down the electric losses into iron loss and copper loss by electromagnetic analysis. Then, focusing on the iron loss that the loss ratio was high, we modified the thickness and material of the stator core sheets and reduced the iron loss in the non-magnetic protection covers of the magnets on the rotor, and thus improved power generation efficiency. Further, we analyzed the flow of magnetic flux and magnetic flux density and found that it would be effective against leakage of the flux between the magnets if we spaced the magnets, which we did and which also allowed us to reduce the amount of magnets used. Furthermore, considering that the generator only turns in one direction, we modified the form of the stator teeth and improved efficiency. Modifying the copper wire diameter and the number of winding of coil to stator pole, while keeping the power generation output also allowed us to reduce the copper loss.To improve fuel efficiency of motorcycles, we focused on the electric losses their generator suffers, identified factors contributing to the losses in existing generators by electromagnetic analysis, and achieved a power generation efficiency of about 80 to 90% or more of the existing generators.