To actuate a looseness preventive mechanism by attaching a coupling member to a member to be fastened.

The coupling member 1 with the looseness preventive mechanism is configured as follows: a male threaded portion 62 of a bolt (first coupling member) 6 is passed through-holes formed in the members to be fastened 3 and 4 to face the bolt 6 through the members 3 and 4, and when fastening to the bolt 6 is established across the members 3 and 4, a resilient member 2 which is set in a groove 14 and bulged from a plane portion 11 while being formed in the plane portion 11 confronting one of the members 3 and 4 abuts to one of the members 3 and 4, and when fastening of the members 3 and 4 by the bolt 6 is completed, a pressure by the resilient member 2 set in the groove 14 is applied to a thread part of the male threaded portion 62 of the bolt 6 such that a friction force of the thread part of the male threaded portion 62 of the bolt 6 increases.