PROBLEM TO BE SOLVED: To rotate and drive one fan forwards and backwards by rotating an engine.SOLUTION: A forward transmission path (S) is constituted by winding a first transmission belt (29) around between a first output pulley (26) that is provided on an input shaft (23) and a first input pulley (28) that is provided on a rotary shaft (27) of a fan (12). A backward transmission path (G) is constituted by winding a second transmission belt (35) around between a second output pulley (33) that is provided on an inverse shaft (32) and a second input pulley (34) that is provided on the rotary shaft (27) of the fan (12). The first transmission belt (29) includes a first tension pulley (40) which connects and disconnects power transmission in the forward transmission path (S). The second transmission belt (35) includes a second tension pulley (41) which connects and disconnects power transmission in the backward transmission path (G).SELECTED DRAWING: Figure 4【課題】エンジンの回転により一つのファンを正逆回転駆動できるものとする。【解決手段】入力軸（２３）に設けた第一出力プーリー（２６）とファン（１２）の回転軸（２７）に設けた第一入力プーリー（２８）との間に第一伝動ベルト（２９）を掛け回して正転伝動経路（Ｓ）を構成し、逆転軸（３２）に設けた第二出力プーリー（３３）とファン（１２）の回転軸（２７）に設けた第二入力プーリー（３４）との間に第二伝動ベルト（３５）を掛け回して逆転伝動経路（Ｇ）を構成し、第一伝動ベルト（２９）に、正転伝動経路（Ｓ）における動力伝達を接続および遮断する第一テンションプーリー（４０）を設け、第二伝動ベルト（３５）に逆転伝動経路（Ｇ）における動力伝達を接続および遮断する第二テンションプーリー（４１）を設ける。【選択図】図４
