Abstract: A cap operating mechanism is adapted to open or close the cap by depressing a push button. Upon depression of a push button 5 against a restoring force of an elastic member 4, a forward end 8b of a push rod member 8 pushes groove 6 serving for cap opening which is located, in this state, at a relatively short distance from the push button 5 and thereby rotates a cap 3 around an axis 2 of a hinged coupler to its opened position. After the push button 5 has been restored under a restoring force of the elastic member 4 to its home position, depressing the button 5 again causes the forward end 8b of the push rod member 8 to push a groove 7 serving for cap closing and thereby rotates the cap 3 around the axis 2 of the hinged coupler to its closed position.