PROBLEM TO BE SOLVED: To obtain a door for separating parent cow and calf, constituted so that parent cow can pass through the door, but calf can not pass through the door.
SOLUTION: This door is opening and closing door for livestock obtained by attaching a door plate capable of each opening and closing to longitudinal both directions on insides of a pair of right and left outer frames 2L and 2R standing in vertical direction. In the door, the door plate is attached through a hinge 4 having habit returning the door plate to closing position to the outer frame and free end sides of right and left door plates 3L and 3R are overlapped by a prescribed width in a state in which mutual inner faces are brought into contact with each other. The door is constituted so that parent livestock pushes door by own force from longitudinal either one of right and left door plates 3L and 3R opens door plate and passes to other side of the door and right and left door plates 3L and 3R immediately returns to close state after passage of parent livestock. The interval of right and left outer frames 2L and 2R are designed to be nearly equal to with of passing parent livestock or to enable transfer control to right and left in order to adjust to the width of parent livestock.