Abstract: A hydroelectric power generation device is structure to utilize water flowing to generate electrical power that could be supplied to a bathroom installation and is generally made up of a functional main body, a battery assembly, and a power generation module. The functional main body has two opposite sides each including a mounting end formed thereon. The functional main body forms therein a receiving chamber. The power generation module includes a stator and a rotor. The rotor is coupled, in a manner of being rotatable, to an axle, which is coupled to a vane wheel. Water flowing into the device drives the vane wheel and the rotor to rotate simultaneously so that magnetic interaction between the rotor and the stator generates electrical power that is supplied to a sensor controlling supply of water flow. A sleeve is fit over the axle for correcting and stably supporting the axle in rotation.