A suction device includes a sucking member having a connecting body connected integrally to a flexible disc body that is disposed under an upright sleeve, a connecting member disposed in the sleeve and connected to the connecting body, an operating member connected to a pivot rod extending through the sleeve, and a cam body accommodated in a cam-accommodating space in the connecting member and pivotable together with the pivot rod. The operating member is operable so as to pivot the pivot rod and the cam body such that an assembly of the connecting member and the connecting body is pulled upwardly by the cam body, thereby forming a vacant space between a central portion of the disc body and a supporting surface to which a peripheral portion of the disc body is attached sealingly.