Abstract: A snow blower auxiliary for a rotary lawn mower easily attachable to the deck of the lawn mower, and which is powered by a drive belt connected to the mower's power shaft which normally would power the mower's cutter blade. The drive belt powers a vertical power shaft of the snow blower auxiliary; and that vertical power shaft passes through a relatively stationary body member through which also passes a horizontal drive shaft which powers the snow blower, and which provides a pressure means by which a spring means is able to swing the vertical power shaft in a manner to exert and maintain the desirable tension in the power belt. The auxiliary thus provides a conversion unit for achieving snow blower operativity of the lawn mower; and it provides advantages of low cost, lack of need of an auxiliary engine means, convenience of storage, off-season usage of the lawn mower's power means, etc.