To provide a flexible coupling which satisfies both requirements, that is, an excellent vibration/sound proof property and a power transmission force.

Elastic members 3A, 3B are interposed between a primary connection elements 13 formed in circumferential direction at predetermined intervals on a primary flange 1 set up on either one of a drive shaft side or a driven shaft side and a secondary connection elements 24 formed in circumferential direction at predetermined intervals on a secondary flange 2 set up on the remaining one of the drive shaft side or the driven shaft side and are located between the primary connection elements 13. The elastic members 3A, 3B fixed on the primary connection elements 13 comprising: a first protrusion 31 which initially contacts with the secondary connection elements 24; a second protrusion 32 which contacts with the secondary connection elements 24 when the first protrusion 31 reaches at predetermined deformation volume; and a relief groove formed therebetween. During the process wherein the elastic members 3A, 3B are subject to a deformation, primarily the first protrusion 31 alone undergoes deformation, and at the time when a torsional angle between the primary and the secondary connection element 13, 24 arrives at predetermined value, the second protrusion 32 also receives deformation, as a result, spring constant increases.