An engagement chain, comprising at least two chain members (12A, 12B) that are capable of selectively advancing and retreating, the two chain members forming a pair, wherein the two chain members are engaged so as to be integrated with each other by moving in an advancing direction and disengaged from each other to bifurcate by moving in a retreating direction from an engaged state in which the chain members are integrated with each other, wherein each of the chain members includes link plates and coupling pins, the link plates each including a first pin hole and a second pin hole arranged in an advancing/retreating direction, the link plates being arranged in series such that the first pin hole of one of the link plates and the second pin hole of an other one of the link plates adjacent to the one of the link plates in the advancing/retreating direction overlap each other, and the link plates being pivotally coupled to each other by the coupling pins inserted through the first pin holes and the second pin holes with the link plates arranged in series, one of the two chain members is referred to as a first chain member and an other one of the two chain members is referred to as a second chain member, the link plates of the first chain member are each referred to as a first link plate and the link plates of the second chain member are each referred to as a second link plate, characterized in that a distance between the first pin hole and the second pin hole of the first link plate is referred to as a first distance and a distance between the first pin hole and the second pin hole of the second link plate is referred to as a second distance, and the first distance is shorter than the second distance the two chain members are engaged so as to be integrated with each other by moving in an advancing direction and disengaged from each other to bifurcate by moving in a retreating direction from an engaged state in which the chain members are integrated with each other, wherein each of the chain members includes link plates and coupling pins, the link plates each including a first pin hole and a second pin hole arranged in an advancing/retreating direction, the link plates being arranged in series such that the first pin hole of one of the link plates and the second pin hole of an other one of the link plates adjacent to the one of the link plates in the advancing/retreating direction overlap each other, and the link plates being pivotally coupled to each other by the coupling pins inserted through the first pin holes and the second pin holes with the link plates arranged in series, one of the two chain members is referred to as a first chain member and an other one of the two chain members is referred to as a second chain member, the link plates of the first chain member are each referred to as a first link plate and the link plates of the second chain member are each referred to as a second link plate, characterized in that a distance between the first pin hole and the second pin hole of the first link plate is referred to as a first distance and a distance between the first pin hole and the second pin hole of the second link plate is referred to as a second distance, and the first distance is shorter than the second distance