The present invention relates to a drive mechanism (10； 177) for a medicament delivery device, which drive mechanism (10； 177) comprises an elongated plunger rod (12； 176), wherein the plunger rod comprises a number of discrete segments (14； 178), interlocking elements (18, 20, 32, 34, 60, 62； 182, 184, 196, 198, 212, 214) arranged between adjacent segments operably arranged to releasably locking adjacent segments, drive force elements (30, 50 71； 194, 210, 230) operably arranged to act between adjacent segments, and release elements (46, 68； 208, 228) operably arranged to act on said interlocking elements (18, 20, 32, 34, 60, 62； 182, 184, 196, 198, 212, 214) such that said segments (14； 178) are released in sequence.
