To provide a chain structure which can easily perform the installation of a chain-tooth jump-out prevention mechanism and position adjustment, and can improve its durability.

The chain structure 40 comprises: a sprocket 4 having pins 10 at it circumference; a chain 12 which is wound to the external periphery of the sprocket 4 and has recesses 14 engaged with the pins 10; and the tooth jump-out prevention mechanism 44 which prevents the recesses 14 from coming off from the pins 10 engaged with the recesses. The tooth jump-out prevention mechanism 44 is arranged outside the chain 12 in the radial direction of the sprocket 4 and has only one tooth jump-out prevention member 44a which is arranged so as to be parallel with the width direction of the chain 12 and in the vicinity of the chain 12.