Abstract: A useful dry battery driven liquid pump for pumping liquid such as kerosene or the like into a tank for an oil heater or the like very conveniently includes a combination of a motor and a liquid pump disposed at the lower end part of a suction tube, a plurality of dry cells contained in a dry battery casing, a liquid surface level detector disposed at the lower end part of a delivery tube and a control circuit which controls operation of the liquid pump properly in response to an output from the liquid surface level detector. The liquid surface level detector includes a prism formed at the lower end of a cylindrical detector body, a light beam generating element and a light beam receiving element. The liquid pump is driven as long as the prism does not get wet with liquid and thus light is reflected from the inner optical surface of the prism toward the light beam receiving element.