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 a needle hub comprising an insertion needle and two spring units assuring automatic insertion and automatic retraction of the insertion needle.The inserter comprises a housing (1), a carrier body (2) carrying an infusion part (8), a needle hub (3), a first moving unit (4) bringing the carrier body (2) to a forward position and a second moving unit (5) bringing the carrier body (2) to a retracted position. The inserter is characterized in that it has means for activation which should be activated at least once in order to bring the carrier body (2) from a retracted to a forward position, and back from the forward to the retracted position.