PURPOSE: To minimize residual grain culms on the side of a ridge when reaping operation is performed toward the side of the ridge.

CONSTITUTION: The objective structure for reaping pretreatment is constructed by forming a link mechanism from an arm member 10 pivoted on the upper part of a stem and culm raising up device 4 so as to enable relative free rocking, a grass dividing tool supporting rod 8 pivoted on the lower part of the stem and culm raising up device 4 so as to enable relative free rocking and the stem and culm raising device 4, simultaneously forming a grass dividing tool 3 installed so as to enable free rocking around the transverse shaft center in the front end of the grass dividing tool supporting rod 8 so as to enable free sliding and guiding in the vertical directions in a sheathing case of the stem and culm raising up device 4 and enabling the free changeover of the stem and culm raising up device 4 and the grass diving tool 3 from the vertically rocked posture for retreat and downward rocked posture for usual use.