In a semiconductor device manufacturing method in which a wafer formed with devices in a plurality of areas sectioned by a plurality of streets formed in a lattice-like pattern on the front surface is divided into the individual devices along the streets, when the wafer is divided into the individual devices by exposing cut grooves formed along the streets by a dicing before grinding process, a rigid plate is applied to the front surface of the wafer and an adhesive film is attached to the rear surface of the wafer. Thereafter, a separation groove forming step is performed in which a laser beam is directed to the adhesive film along the cut grooves form the dicing tape side applied with the wafer attached with the adhesive film to form separation grooves in the adhesive film along the cut grooves.