The purpose of detection by the board detection sensors will be described. Board detection sensor S1 detects that board 14 enters carry-in conveyor 6 from the upstream device. Board detection sensor S2 detects presence or absence of board 14 of a standby state in the delivery of board 14 from carry-in conveyor 6 to work station conveyor 7#1. Board detection sensor S3 provided in work station conveyor 7#1 is at a stop position at the time of positioning board 14 in work station [A1] and detects a tip of board 14 reached the stop position. Board detection sensor S4 is disposed in a downstream of board detection sensor S3 by a predetermined distance. It is detected whether or not board 14 is in an overrun state from the normal stop position by presence or absence of the detection of board 14 by board detection sensor S4.

Board detection sensor S5 and board detection sensor S6 provided in work station conveyor 7#2 have the same function as that of board detection sensor S3 and board detection sensor S4 in work station [A1]. Board detection sensor S7 provided in carry-out conveyor 8 detects that board 14 enters carry-out conveyor 8 from work station conveyor 7#2. Board detection sensor S8 detects that board 14 is discharged from carry-out conveyor 8.