An inclined slope face portion is formed on a top face of a box member. This slope face portion has a downward gradient from a side wall of a box-pin-insertion hole up to a side wall of an insert-pin-insertion hole. The insert pin is inserted into the box member in which the box pin is inserted and fixed in a box-pin-insertion hole thereof. Then, when a rear end portion of a slider is brought into contact with the box member, the slider is inclined relative to the box member. Although conventionally, the insert pin was inserted into the insert-pin-insertion hole of the box member from just above the box member, this invention allows the insert pin to be inserted obliquely from above the box member. Therefore, the insertion operation can be carried out smoothly and easily. Thus, the slider is disposed in an inclined posture relative to a box member of the separable bottom stop assembly so as to achieve a smooth operation for inserting the insert pin.