PURPOSE: To enable the check of the positional deviation of a lead frame to be enhanced in precision by a method wherein a lamp and a camera are provided to a die unit used for the forming of a lead, the position of a pitch hole of the lead frame is detected by the light and the camera, and the amount of deviation is detected by image processing.

CONSTITUTION: A lamp 18 and a camera 19 provided to a forming die of a semiconductor device 1 to detect the position of pitch holes of a lead frame, a semitransparent plate 21 used for the formation an image, an image processor 20 which processes the position data of the pitch holes of the lead frame 5, and others are provided. At the positioning of a lead when the semiconductor device 1 is formed, the pitch hole of the lead frame 5 is irradiated with light emitted from the lamp 18 of one of the dies through a small hole provided to the die concerned, the image of a pitch hole is formed on the semitransparent plate 21 provided to the other die and picked up by the camera 19, and then the amount of the positional deviation of the pitch hole is detected by the image processor 20. By this setup, the amount of deviation can be numerically detected high in accuracy.