PROBLEM TO BE SOLVED: To provide a bone anchor unit for spinal fusion which has a reduced number of parts thereby enabling complication of the structure thereof to be suppressed and in which an arrangement direction of a rod member with respect to a housing member can be easily defined, thereby enabling the rod member to be easily set and firmly fixed and the structure of an insert member is simplified, and which can be easily assembled.SOLUTION: A circumferential groove 17 is formed in the inner periphery of the housing member 13. The insert member 12 includes a convex projection 24 engageable with the circumferential groove 17 and a flexible part 23 with the projection 24 on the end side. The insert member 12 is retained rotatably with respect to the housing member 13 in a state in which the convex projection 24 is engaged with the circumferential groove 17. When the insert member 12 is pushed into the housing member 13 to bend the flexible part 23, the engagement of the projection 24 with the circumferential groove 17 is released and the convex projection 24 is engaged with an engaging concave dent part 18 of the housing member 13.
