PURPOSE: To improve the productivity in a conveyor system by making the conveyor belt of a tact transport device for assembly from metal and intermittently and reducing the tact time and eliminating the position deflection of a work due to the stop shock.

CONSTITUTION: A circulating transport device consists of a tact transport device 1 for assembly, transfer device 2 for unloading, transport device 3 for return, and a transfer device 4 for loading. When a work pallet P reaches a transport starting edge station S0, an unclamp releasing operating device 11 operates to turn an unclamp holding device 9 in the E direction. Since a clamp 7 for transport tightens the attachment 36 of a chain 6 at this time, the pallet P having a work loaded is transported intermittently in the integral form with the chain 6. Though the pallet P stops at each station S, the need of setting the length taking account of the excess portion can be avoided, since the metal transport body 6 does not extend nor contract.