A batteryless engine system characterized by comprising: a fuel tank for containing fuel; an internal combustion engine; a generator that is driven by the internal combustion engine and produces electric power; a recoil starter for starting the internal combustion engine; a control unit that operates with electric power generated by the generator; an injector that operates with electric power generated by the generator, is controlled by the control unit, and supplies fuel to the internal combustion engine; a fuel pump that operates with electric power generated by the generator, is controlled by the control unit, and supplies fuel contained in the fuel tank to the injector; an ignition apparatus that ignites fuel compressed in the internal combustion engine; a power supply line that supplies electric power generated by the generator to the ignition apparatus, the injector, and the fuel pump; a switch provided for the power supply line, the switch being switched from OFF to ON when electric power generated by the generator is supplied to the ignition apparatus, the injector, and the fuel pump, and the switch being switched from ON to OFF when electric power generated by the generator is not supplied to the ignition apparatus, the injector, and the fuel pump; and a detection unit (7; 21) that detects a number-of-rotations of the internal combustion engine, characterized in that, in a starting period of the internal combustion engine, which is started using the recoil starter, the control unit obtains acceleration from the number-of-rotations detected by the detection unit, determines whether or not the internal combustion engine can perform self-sustaining rotation based on the number-of-rotations and the acceleration, and if the internal combustion engine cannot perform self-sustaining rotation due to the number-of-rotations being less than a prescribed number-of-rotations at which the internal combustion engine can perform self-sustaining rotation, or the acceleration being greater than or equal to a prescribed acceleration, reduces a load for the recoil starter by not supplying electric power from the generator to the ignition apparatus, the injector, and the fuel pump by maintaining the switch being OFF, and if the internal combustion engine can perform self-sustaining rotation, due to the number-of-rotations becoming greater than or equal to the prescribed number-of-rotations at which the internal combustion engine can perform self-sustaining rotation and the acceleration being less than the prescribed acceleration, supplies electric power from the generator to the ignition apparatus, the injector, and the fuel pump by switching the switch from OFF to ON. a fuel tank for containing fuel; an internal combustion engine; a generator that is driven by the internal combustion engine and produces electric power; a recoil starter for starting the internal combustion engine; a control unit that operates with electric power generated by the generator; an injector that operates with electric power generated by the generator, is controlled by the control unit, and supplies fuel to the internal combustion engine; a fuel pump that operates with electric power generated by the generator, is controlled by the control unit, and supplies fuel contained in the fuel tank to the injector; an ignition apparatus that ignites fuel compressed in the internal combustion engine; a power supply line that supplies electric power generated by the generator to the ignition apparatus, the injector, and the fuel pump; a switch provided for the power supply line, the switch being switched from OFF to ON when electric power generated by the generator is supplied to the ignition apparatus, the injector, and the fuel pump, and the switch being switched from ON to OFF when electric power generated by the generator is not supplied to the ignition apparatus, the injector, and the fuel pump; and a detection unit (7; 21) that detects a number-of-rotations of the internal combustion engine, characterized in that, in a starting period of the internal combustion engine, which is started using the recoil starter, the control unit obtains acceleration from the number-of-rotations detected by the detection unit, determines whether or not the internal combustion engine can perform self-sustaining rotation based on the number-of-rotations and the acceleration, and if the internal combustion engine cannot perform self-sustaining rotation due to the number-of-rotations being less than a prescribed number-of-rotations at which the internal combustion engine can perform self-sustaining rotation, or the acceleration being greater than or equal to a prescribed acceleration, reduces a load for the recoil starter by not supplying electric power from the generator to the ignition apparatus, the injector, and the fuel pump by maintaining the switch being OFF, and if the internal combustion engine can perform self-sustaining rotation, due to the number-of-rotations becoming greater than or equal to the prescribed number-of-rotations at which the internal combustion engine can perform self-sustaining rotation and the acceleration being less than the prescribed acceleration, supplies electric power from the generator to the ignition apparatus, the injector, and the fuel pump by switching the switch from OFF to ON.