To solve a problem of a conventional changing-over lever wherein the change-over lever rotates with a fulcrum as a center by finger pressing, and therefore, as the changing-over lever is rotationally moved, contact areas of the finger with a lever (arm) section of the changing-over lever is gradually decreased, thereby making the fingers to gradually become slippery on the changing-over lever, preventing reliable finger pressing.

The changing-over mechanism is provided with a finger-touching plate upper cover 58, a finger-touching plate main body 67, a lever shaft 66 built-in the finger-touching plate main body 67, a lever arm 53 having a small recessed section 51 turnably engaged with the supporting shaft 59 at one end portion thereof and a large recessed section 52 engaged with a protruding section of a rack 22 at the other end thereof, a link arm 54, and a pin shaft 57 engagedly fixing the link arm 54 to a link arm receiving section 68 of the finger-touching plate main body 67. The finger touching plate main body 67 is translated (parallel slides) downward while being substantially parallel maintained.