A supercharging system for a combustion engine of a motorcycle includes a supercharger which pressurizes intake air and supplies the intake air to the combustion engine, an air intake chamber which is connected to downstream of the supercharger, a relief passage which relieves the high-pressure intake air within the air intake chamber, and a relief valve which is provided on the relief passage. The air intake chamber is disposed above the combustion engine, and the relief passage is disposed below an upper end of the air intake chamber. The relief passage is connected to a front surface of the air intake chamber.