PURPOSE: To ensure excellent sealing performance over a long period by forming a shutoff element causing a pressure reducing effect from a material having a hardness higher than a seat material for sitting the shutoff element.

CONSTITUTION: In a quick coupling element 2 in which a ball 8 is pressed to a seat 9 by the pressure reducing effect caused in the ball 8 as a shutoff element and the spring force of a spring 10, one end of the spring 10 is supported by a bush 11 to transmit the spring force to the ball 8 through a force transmitting member 12. The ball 8 is driven through an operating member 13 in relation to the mechanical operation of a valve body 1 by a second part 14 displacing in the longitudinal direction of the coupling element 2. The ball 8 has a hardness substantially exceeding the hardness of the material of the seat 9, so that the sealing effect is caused between the ball 8 and the seat 8 by the natural elasticity of the seat 9.