A hand tool includes a housing defining a receiving space, a shaft rotatably extending through the receiving space and having opposite end portions that are exposed from the housing, a ring-shaped flywheel disposed rotatably in the receiving space and surrounding the shaft, and a speed-increasing gear mechanism. The gear mechanism includes a start gear coupled co-rotatably to the shaft and disposed in the receiving space, at least one transmission gear rotatably disposed in the receiving space and meshing with the start gear, and a final gear coupled co-rotatably to the flywheel, disposed in the receiving space and meshing with the transmission gear. A rotational speed of the final gear is greater than that of the start gear.