There is provided a driving control device of an opening and closing body, which drives the opening and closing body in a closed state by a motor through an idling section thereof. The device includes a calculation section for calculating a rotation speed difference between a rotation speed of the motor in the idling section and a current rotation speed of the motor; and an insertion detection section for detecting insertion of a foreign member based on the calculated rotation speed difference and a predetermined threshold value. The threshold value monotonously decreases according to an increase in the rotation amount of the motor to coincide with a fully-closed state threshold value at a predetermined rotation amount of the motor within an error range of the rotation amount corresponding to the fully-closed state, and to maintain the fully-closed state threshold value to a maximum rotation amount in the error range.