An interlocking chain unit comprising a pair of interlocking chains (110A, 110B), wherein the pair of interlocking chains (110A, 110B) includes a first interlocking chain and a second interlocking chain, each of which includes outer tooth link plates (112, 112X,112AY, 112BZ, 112C, 112D) each having a hook-shaped interlocking end face (112F, 112AF, 112BF, 112CF, 112DF) and a buckling restricting end face (111S, 112S, 112BS, 112CS), pairs of front and rear coupling pins (113, 113B1, 113B2, 113C1, 113C2, 113D2) fitted to the outer tooth link plates (112, 112X, 112AY, 112BZ, 112C, 112D), and inner tooth link plates alternately placed with the outer tooth link plates (112, 112X, 112AY, 112BZ, 112C, 112D) in a state of being loosely fitted to the coupling pins (113, 113B1, 113B2, 113C1, 113C2, 113D2), the first interlocking chain and the second interlocking chain are interlocked with each other to form a rigidified chain portion, and are disengaged from each other to bifurcate, the interlocking chain unit being characterized in that a link plate of the first interlocking chain that is one of the inner tooth link plates and the outer tooth link plates (112, 112X, 112AY, 112BZ, 112C, 112D) of the first interlocking chain and is in a state immediately before completion of an interlocking operation when the first interlocking chain is rotated around the preceding coupling pin (113, 113B1, 113B2, 113C1, 113C2, 113D2) in the forward and backward direction of the rigidified chain portion is defined as a first link plate, a link plate of the second interlocking chain that is located subsequent to the first link plate is defined as a second link plate, the second link plate having a disengagement-side coupling pin (113B1), a link plate that is located subsequent to the second link plate is defined as a third link plate, the third link plate having a disengagement-side coupling pin (113C1) and a coupling pin (113C2) that faces the disengagement-side coupling pin (113B1) of the second link plate, and the interlocking operation between the first link plate and the second link plate is completed such that a first inter-pin distance between the disengagement-side coupling pin (113B1) of the second link plate and the coupling pin (113C2) facing the disengagement-side coupling pin (113B1) of the second link plate is made substantially equal to a second inter-pin distance in the rigidified chain portion, and a third inter-pin distance between the disengagement-side coupling pin (113C1) of the third link plate and a coupling pin (113D2) that faces the disengagement-side coupling pin (113C1) of the third link plate is made to approach the second inter-pin distance in the rigidified chain portion, and wherein when the first inter-pin distance and the third inter-pin distance become equal to the second inter-pin distance in the rigidified chain portion in the process of reaching the position of the first link plate from the position of the third link plate at the time of the interlocking operation, any or all of the inner tooth link plates, the outer tooth link plates (112, 112 X, 112AY, 112BZ, 112C, 112D), and the coupling pins (113, 113B1, 113B2, 113C1, 113C2, 113D2) are elastically deformed in a state of balancing a force acting on the hook-shaped interlocking end faces (112F, 112AF, 112BF, 112CF, 112DF) interlocked with each other and a force acting on the buckling restricting end faces (111S, 112S, 112BS, 112CS) connecting each other.