PURPOSE: To make it possible to follow size reduction of a semiconductor element by providing a mask to a place excepting resin burr fixing between a lead led out of sealing resin and the sealing resin and excepting a specified place of a reinforcement fine line and by cutting the reinforcement fine line and the resin burr by irradiating laser.

CONSTITUTION: A semiconductor device which is mounted on a lead frame with a reinforcement fine line 7 is sealed with resin 2. A mask 5 is provided to a place excepting resin burr 8 fixing between a lead 9 led out of the sealing resin 2 and the sealing resin 2 and excepting a specified place of the reinforcement fine line 7. Laser is irradiated to the reinforcement fine line 7 and the resin burr 8 to cut them. For example, YAG laser light is radiated from a laser light generator 3, bent by 90° by a laser light bending part 4 consisting of prism and reaches the mask 5. Diameter and focus of YAG laser light which passed through the mask 5 are adjusted by a converging part 6 and energy per a unit area is increased. Thereby, a processing object is fused.