A manually operated pump for supplying air to a bicycle comprises an outer tube with one end closed and the other end open. A core tube slides in the outer tube and has a piston assembly on one end and an end socket on the other. There is a hose which slides in the core tube. One end of the hose is connects with an air needle, and the other end connects with an air nozzle assembly. The piston assembly comprises a piston, a piston ring, and a one-way valve communicating with the core tube and the outer tube. A narrowing port is formed in the end socket of the core tube. A foot stand is hinged on an outer side of the end socket of the core tube. The air needle has a head matching the narrowing port.