The present invention concerns a drug delivery device (1) comprising: a housing (2) extending along a main axis, a torsion spring (5) comprising a first spring end (4) arranged stationarily with respect to the housing (2) and a second spring end (6) capable of rotation about the main axis, a rotatable shaft (80) extending along the main axis, the rotatable shaft (80) having a non-self-locking thread (81) and being axially fixed with respect to the housing (2), a spring end retainer (82) to which the second spring end (6) is attached, the spring end retainer (82) being rotationally fixed relative to the rotatable shaft (80), and a nut member (45) engaged with the non-self-locking thread (81), the nut member (45) being axially movable by translation relative to the housing (2) to thereby travel the non-self-locking thread (81) between a first position in which the torsion spring (5) is in a relaxed state and a second position in which the torsion spring (5) is in a strained state.
