The invention relates to an autoinjector (1) comprising: a case (2) adapted to hold a medicament container having a needle (4)； a needle shroud (7) telescopically coupled to the case (2) and movable between a first extended position (FEP) relative to the case (2) in which the needle (4) is covered and a retracted position (RP) relative to the case (2) in which the needle (4) is exposed； and a plunger (10) rotationally and slidably disposed in the case (2), the plunger (10) rotatable relative to the case (2) between a first rotational position in which the plunger (10) is engaged to the case (2) and a second rotational position in which the plunger (10) disengages the case (2), wherein the needle shroud (7) engages the plunger (10) to rotate the plunger (10) from the first rotational position to the second rotational position when the needle shroud (7) translates from the first extended position (FEP) to the retracted position (RP), the auto-injector (1) further comprising: a cap (11) removably coupled to the case (2), wherein the cap (11) includes at least one compliant case beam (11.6) adapted to releasably engage at least one aperture (2.16) in the case (2).本發明係有關於一種自動注射器，其包含：一外殼，其適用於固持具有一針頭的一藥劑容器；一針罩，其伸縮地與該外殼耦合並可在相對於該外殼的一第一延伸位置與一縮回位置之間移動，在該第一延伸位置中該針頭被覆蓋，而在該縮回位置中該針頭係為露出；一柱塞，其轉動地且滑動地配置在該外殼中，該柱塞可相對於該外殼在一第一轉動位置與一第二轉動位置之間轉動，在該第一轉動位置中，該柱塞係與該外殼嚙合的，而在該第二轉動位置中，該柱塞係與該外殼脫離的；其中該針罩與該柱塞嚙合以當該針罩由該第一延伸位置移動至該縮回位置時，將該柱塞由該第一轉動位置轉動至該第二轉動位置，該自動注射器進一步包含：一蓋，其可移開地與該外殼嚙合，其中該蓋包括至少一順應式(compliant)外殼樑其適用於可鬆開地與該外殼中至少一孔口嚙合。
