PURPOSE: To improve the durability of a relaying gear, etc., by reducing the bearing radial load of gear trains due to a reel taking-up load in the reel base driving device of a magnetic recording and reproducing device.

CONSTITUTION: An arm driving plate 36 moving in accordance with a reproduction mode or FF/REW modes is provided in this device and a rotational arm 34T and one end of a first arm 42 are connected via an engaging shaft 35T. Then, the other end of the arm 42 is held freely rotatably at a supporting shaft 41 and a second arm 43 is held freely rotatably around the supporting shaft 41 as the center. The counterclockwise rotational force is imparted to a arm 43 with respect to the arm 42 by hooking a twisting coil spring 46 to arms 42, 43. In such a manner, a roller 44 mounted on the arm 43 is made to abut on the outer peripheral part of a reel base bearing 45 only in the case of the FF mode to reduce the rapid increase of the bearing radial load loaded on a FF idler gear right after the changeover of the mode.