PURPOSE: To prevent accident by furnishing sensors on two points on a transport belt, which are to sense a lead frame on the belt, and thereby actuating alarm when a jam occurs.

CONSTITUTION: A lead frame 2 is transported by a transport belt 4 into a cassette 1. When sensors 6, 7 sense the lead frame 2, a signal is given to a processing device 8. If the front edge of a lead frame 2 is unintentionally detained at the inlet to cassette 1, the sensor 6 continues to emit the ON signal to allow a timer in connection with the processing device 8 to know the specified time so as to stop the belt 4. Thus occurrence of a trouble is informed. In case the lead frame 2 is detained within cassette 1, a load sensor furnished at a detent member 12 senses that the load on a spring 13 has increased, so as to the belt 4 and an intrusion mechanism 9. Thus propagation of the occurrence to accident can be prevented.