A power transmission roller assembly arranged between a driving roller and a driven roller so as to transmit a rotational force of the driving roller to the driven roller due to a frictional force, characterized in that the power transmission roller assembly comprises a power transmission roller retained by a receiving member, and configured to be brought into and out of contact with the driving roller and the driven roller; a pivot shaft fixed to a vehicle body; a pivot arm arranged radially inside of the power transmission roller, and pivotally mounted on the pivot shaft; a roller support bearing rotatably supporting the power transmission roller; a pair of biasing members including, respectively, shafts fixed to the pivot arm, and elastic members each arranged coaxially with a corresponding one of the shafts and biasing the receiving member such that the receiving member is moved away from the pivot arm, the biasing members biasing the roller support bearing to a predetermined position between the driving roller and the driven roller such that an abutment force between the driving roller and the power transmission roller is balanced with an abutment force between the driven roller and the power transmission roller; and sliding members mounted on the respective shafts such that the shafts extend through the sliding members, the sliding members being kept in abutment with the receiving member due to biasing forces of the elastic members, wherein the sliding members are configured such that by the biasing forces of the elastic members, and a reaction force applied from the receiving member in a direction opposed to a direction of the biasing forces of the elastic members when the receiving member is displaced toward the pivot arm, the sliding members are pressed in opposed axial directions of the shafts, and deformed toward the shafts such that frictional forces are generated between the sliding members and the respective shafts. a power transmission roller retained by a receiving member, and configured to be brought into and out of contact with the driving roller and the driven roller; a pivot shaft fixed to a vehicle body; a pivot arm arranged radially inside of the power transmission roller, and pivotally mounted on the pivot shaft; a roller support bearing rotatably supporting the power transmission roller; a pair of biasing members including, respectively, shafts fixed to the pivot arm, and elastic members each arranged coaxially with a corresponding one of the shafts and biasing the receiving member such that the receiving member is moved away from the pivot arm, the biasing members biasing the roller support bearing to a predetermined position between the driving roller and the driven roller such that an abutment force between the driving roller and the power transmission roller is balanced with an abutment force between the driven roller and the power transmission roller; and sliding members mounted on the respective shafts such that the shafts extend through the sliding members, the sliding members being kept in abutment with the receiving member due to biasing forces of the elastic members, wherein the sliding members are configured such that by the biasing forces of the elastic members, and a reaction force applied from the receiving member in a direction opposed to a direction of the biasing forces of the elastic members when the receiving member is displaced toward the pivot arm, the sliding members are pressed in opposed axial directions of the shafts, and deformed toward the shafts such that frictional forces are generated between the sliding members and the respective shafts.