To provide a rotary driving device which can easily ensure a large rotation driving torque even in electric toys of which the spacial constraint is strict such as a remote-controlled tank.

This rotation driving device rotates and drives a rotator B which is freely rotatably supported on a stator A by a motor 15 which is provided in the stator A. In the rotation driving device, an inner cover style gear holder 30 which covers and is fixed to a chassis 10 along the internal surface of a cover 20 is provided between the chassis 10 which constitutes the stator A and the cover 20. The gear holder 30 freely rotatably supports a two-stage gear 44 for which a smaller-diameter gear is combined on a larger-diameter gear, on the upper surface. The larger-diameter section of the two-stage gear 44 which is supported by the gear holder 30 is engaged with a gear 43 in the chassis 10, and the smaller-diameter section of the two-stage gear 44 penetrates the cover 20 and is engaged with a gear b in the rotator B.