An operation unit includes a lever shaft having an operating lever at one end thereof and orthogonal to the operating lever, a plate with a flange having a bearing of the lever shaft, the other end-side of the lever shaft being arranged with penetrating the plate with a flange from a front surface thereof, a rotation restraint part for the lever shaft fixed to the lever shaft behind the plate with a flange and having a self-return function of forward and reverse rotations of the lever shaft, a cover with a flange covered on a backside of the plate with a flange in a form of sandwiching the rotation restraint part, a tip end-side of the lever shaft penetrating the cover with a flange via a bearing, and a potentiometer provided on a backside of the cover with a flange, rotation of the lever shaft being transmitted to the potentiometer.