Abstract: A small-sized hydroelectric power generating apparatus includes a body case having a fluid passage, a water wheel provided at the above fluid passage and rotating with passing of the fluid having the predetermined flowing amount, a rotator coupled to this water wheel, and rotating with the water wheel, the rotator serving as a rotor portion arranged opposed to a stator portion, the rotor portion being relatively rotated in relation to the stator portion by passing the fluid to generate electric power, the stator portion having comb-shaped pole teeth which are arranged in the circumferential direction at regular intervals so as to be opposed to the peripheral surface of a rotor magnet of the above rotor portion, and a circumferential gap between the adjacent pole teeth is set to 1.5 times or less the size of a radial gap between each pole tooth and the rotor magnet.