A pad structure includes a main body made of soft material. The main body has an axial surface, a suction surface, and a peripheral surface. The axial surface is provided for being pressed by a pressing member of the sucking disc. The suction surface is provided for sucking on a target object. The axial surface includes a lifting portion and a pressure bearing block. The pressure bearing block is hard and circular shaped. The portion of the main body between the lifting portion and the pressure bearing block is defined as a deformable portion. The portion of the main body below the pressure bearing block is defined as an undeformable portion. The undeformable portion is located at the outer periphery of the main body. The deformable portion is located between the lifting portion and the undeformable portion.