To provide a device for dividing a woody board which prevents a piercing injury by a piercing body from remaining in a divided thin board when the woody board is divided in the thickness direction into two parts.

In the dividing device, a pair of small diameter rolls 1 and 1 is set on both sides of the passage of the woody board. Large diameter rolls 2 and 2 which regulate the deflection of the small diameter rolls 1 and 1 at least in the vertical direction of the passage and migration regulating members 3 and 3 which regulate the forward/backward migration in the advance direction of the woody board 6 of the small diameter rolls 1 and 1 are installed in each small diameter roll 1 or 1. In addition, driving members 4 and 4 which rotate/drive the small diameter rolls 1 and 1 in a prescribed direction through the large diameter rolls 2 and 2 are installed. A division blade 5 having an edge part in an appropriate shape is set at a position where the edge 5a turned in the reverse direction to the advance direction of the woody board 6 is seen in a divided shape at the outlet of the passage of the woody board.