To provide a tension device capable of adjusting tension of an endless belt to be used for physical distribution conveyance or power transmission by a simple mechanism and a simple operation in a single operation.

When tension of an article conveying or power transmitting belt 30 which moves and travels is adjusted, a roller shaft 22 to be fixed by one fixing bolt 21 in the position deviated from the central axis C-C by the eccentricity (h) is provided to an attaching part 50, and a pair of right and left position adjusting holes 23 are provided on the roller shaft 22. Moreover, a tension roller 25 is rotatably supported on the outer periphery of the roller shaft 22 through bearings 24 and brought into contact with one surface of the belt 30, and torque is applied by frictional force.