PURPOSE: To aim at efficient tuning and synchronous operations on the plural number of hydraulic motors, by feeding the oil leaked out of the drains of each hydraulic motor driving conveyor rollers connected in series, to the ensuing hydraulic motors in regular sequence.

CONSTITUTION: When a conveyed article 10 is transferred from a hydraulic roller to the counterpart II, a hydraulic motor 12 is heavily loaded out, while a hydraulic motor 14 is lightly loaded. In this case, drain flows D1, D2 of these hydraulic motors 12 and 14 come to D1D2 and in the hydraulic motor 14, if cracking pressure is of R4>C4=C3 (R4: setting pressure of relief valve, C4: setting pressure of check valve at tank port side, C3: setting pressure of check valve at pressure port side), the oil leaked owing to the magnitude of load in the hydraulic motor 12 is fed to a pressure port P2 via a check valve 16 of the hydraulic motor 14. As a result, the hydraulic motor 14 achieves its tuning and synchronous operations without producing cavitations.