The invention relates to an inserter for an infusion set for intermittent or continuous administration of a therapeutical substance, such as e.g. insulin. The inserter comprises means for insertion and retraction of an introducer needle. With an inserter device according to the invention it is possible to introduce an insertion needle when placing a medical device sub- or transcutaneously. The Inserter device comprises a housing (1, 2, 12) which hides the insertion needle (7, 17) before insertion and can hide the insertion needle (7, 17) after insertion and placing of the medical device. The insertion needle (7, 17) moves relative to the housing (1, 2, 12) toward the patients skin surface during insertion and the inserter device comprises a bi-stable elastic element (1, 11) having two equilibrium states.
