An object of the present invention is to secure the good discrimination of the operation depth adjusting switch provided on the grip portion of the operation lever and to prevent the operation by the thumb of the hand holding the operation lever from being performed in a state in which there is little possibility of causing erroneous operation . The operation lever 42 of the operation lever which can be moved in the forward and backward directions is classified by arranging the operation depth adjusting switch 42 in the vertical direction on the lateral side 44A located on the steering seat side in the lateral direction, The depth adjusting operation switch 42 is a direction in which the pressing operation direction a of one operation switch 42 is vertically spaced with respect to the pressing operation direction b of the other operation switch 42, And the pressing operation direction b of the other operation switch 42 is a horizontal direction or a direction apart from the vertical direction with respect to the pushing operation direction a of the one operation switch 42. [ In addition, the present invention makes it easy to grasp the relative positional relationship between the grip portion and the operation switch even when the operation lever is not visible, so that the operation by the thumb of the hand holding the operation lever can be easily performed Respectively. The grip portion 40 of the operation lever which can be moved in the forward and backward directions is provided with the operation switch 42 for adjusting the dropping depth on the lateral side 44A located on the side of the steering seat in the lateral direction, And the concave portion 46 is formed at a position near the side of the side surface 44A on which the operation switch is disposed. Is formed so as to face the thumb convex portion of the hand gripping the grip portion (40) so as to be able to operate the switches (42, 42). Further, a problem to be solved by the present invention is to
