The present invention relates to a drug delivery device (1) with a power unit (10, 110, 210, 310) adapted to release energy for inducing relative rotation between a first interface portion (45) of the drug delivery device (1) and a second interface portion (22) of the drug delivery device (1). The power unit (10, 110, 210, 310) comprises a first spiral spring member (15, 15, 215, 315) and a second spiral spring member (16, 116, 216, 316) arranged in series along an axially extending structure (11 111 211, 285, 281 311, 385, 1381, 386, 381).
