To miniaturize a worm gear type step-up/reduction gear converting friction transmission between gear tooth surfaces into rolling transmission of rollers by increasing the number of the rollers on a second shaft side simultaneously engaged with a spiral groove of a first shaft to reduce a load of a roller.

This step-up/reduction gear includes the first shaft formed with the spiral groove therein and the second shaft including the rollers rotatably supported on a plurality of pivots projectingly provided in a flange part. The first shaft is arranged nearer a center of the second shaft than pitch circles at distal ends of the pivots to engage the spiral groove with the plurality of rollers.