A chuck table holds a workpiece having a warp. The chuck table includes a suction holding member having a suction holding surface for holding the workpiece under suction, and an annular seal member provided around the outer circumference of the suction holding member for supporting a peripheral portion of the workpiece. The annular seal member is formed from an elastic member. The upper surface of the annular seal member is set higher in level than the suction holding surface according to the warp of the workpiece. In holding the workpiece on the chuck table under suction, vacuum leaking from the gap between the workpiece and the suction holding surface due to the warp of the workpiece is applied to the space defined by the workpiece and the annular seal member, thereby elastically deforming the annular seal member to flatten the upper surface of the workpiece.