A transfer system includes transfer lines (L) each of which forms a closed loop and has transfer-in stations (S1 and S3) and transfer-out stations (S2 and S4) for assembling parts to a work, while circulating the work along the transfer line (L); and a work and part transfer passage (51) for transferring the work and the parts. Transfer-in stations (S1 and S3) and the transfer-out stations (S2 and S4) are disposed at each of the longitudinal ends of each of the transfer lines (L). Sub-transfer-passages (521 and 522) branching out rightward and leftward from the work and part transfer passage (51), are disposed along longitudinal sides of the transfer lines (L). With this layout, a plurality of the transfer lines (L) can be disposed in a required minimum space, while securing a smooth supply and discharge of the works and parts with respect to the plurality of the transfer lines L.