PURPOSE: To rotate a conveyance roller for a substance to be conveyed independently from a gear train at a front stage where occasion demands by a method wherein the shaft of a second gear is rotatably held around the shaft of a third gear and the second gear is energized in the direction in which the second gear is engaged with first and third gears.

CONSTITUTION: The shaft 80 of a second gear 62 is supported rotatably around the shaft 83 of a third gear 61 by means of a support means 81 and the second gear 62 is energized through the force of a spring 86 in a direction in which the second gear is engaged with first and third gears 63A and 61. The rotation output of a motor is exerted on the third gear 61 and by rotationally driving rollers 45A and 45B based on rotation of the first gear 63A, the rollers 45A and 45B are easily rotatable independently from a front stage gear train where occasion demands. As noted above, by nipping a substance 43 to be conveyed as rotational drive is effected, the rollers 45A and 45B to exert a driving force on the substance 43 to be conveyed and convey it are easily rotated independently from front and rear gear trains where occasion demands.