PURPOSE: To strengthen the mounting and holding force of a spring seat and compact a buffer device by interposing a fixed member having a square section between a projection formed around the periphery of a buffer body and a section engaging therewith.

CONSTITUTION: A buffer body is formed on the outer tube 1 with a projection 10, and a spring seat 11 is formed on the upper side portion with first and second engaging section 17, 18. A ring-like fixed member 19 having a square section is interposed between the shoulder 15 of the projection 10 and the second engaging section 18 to mount the lower corner 20 on the shoulder 15 of the projection 10 and the second engaging section 18 on the upper corner 21. An external force, if applied to the spring seat 11, is transmitted to the fixed member 19 so that the corner 20 is included in the shoulder 15 while the corner 21 is included in the second engaging section 18 to fix surely the fixed member 19 to the outer tube 1. Thus, the spring seat 11 can be mounted to the buffer body with a large supporting force to compact the device.