A liquid cooling system for cooling a high heat generating body, such as a semiconductor element or the like, of the type used in an electronic apparatus that is small and thin in size, or in a personal computer equipped with such a structure therein. The system has a pump of the reciprocal movement type, a heat receiving jacket, a heat radiation pipe, and a connector pipe for connecting those parts with one another so as to form a closed loop filled with a cooling liquid. In the system, &Dgr;Vs is equal to or greater than &Dgr;Vp, wherein the inner volume change when the pump emits pulsation therefrom is &Dgr;Vp, the pressure caused by the volume change is P, and the volume change due to the pressure P that occurs in flow passage of the cooling liquid &Dgr;Vp other than within the pump, is &Dgr;Vs.