A secondary battery including: an electrode assembly including a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate; a can accommodating the electrode assembly and an open end; and a cap assembly to seal the open end of the can. A well flow regulating system includes a flow regulator for regulating a flow rate of a fluid in a wellbore, the flow rate remaining substantially constant while a differential pressure across the flow regulator varies. Application in hairdressing facilities. The diaphragm is formed to make maximum a difference in air pressure of the front surface and the rear surface of the diaphragm, thereby forming any one of concave and convex shapes thereof. The hydraulic fluid system includes a power piston reciprocable in the power cylinder.