Abstract: A check valve structure includes an engaged portion including a hole for ventilating fluid between one side and another side of the engaged portion, and a hole plug. The hole includes a locking hole and a ventilating hole outwardly circumferentially arranged around the locking hole. The hole plug includes a locking portion inserted in the locking hole to lock the locking portion therein and an outer portion outwardly circumferentially extending from the locking portion to cover the ventilating hole such that the fluid flows in a direction from the one side to the another side, and is prevented from flowing in a direction from the another side to the one side.