To provide a suction cup that prevents sideways slip of a stool for stabilization thereof when the stool is disposed for reducing a step in a wet place such as a bathroom.

After pressing the suction cup against an object to which the suction cup is adhered, a suction force generated by a pressure difference between the pressure within the suction cup and the atmospheric pressure in an unloaded adhesion state, is utilized to press and flatten out a first sideways slip preventing part provided along the circumference of an inner spherical surface side end of a bowl lid-like portion against the object to which the suction cup is adhered with the strong suction force. As a result, high surface pressure is generated in the first sideways slip preventing part and a sideways slip preventing effect can be obtained. In addition, water between the suction cup and the object to which the suction cup is adhered is eliminated so as to prevent a coefficient of friction from being decreased. In a loaded state, second sideways slip preventing parts provided on the inner spherical surface side of the bowl lid-like portion are pressed and flattened out by the load so as to generate a high surface pressure in the second sideways slip preventing parts, thus preventing the sideways slip.