A medicament delivery device, which comprises a driving mechanism and a housing (1) having a reservoir (2), which is at least partly filled with a substance and which is sealed at least on one side with a flexible wall (21). The driving mechanism is adapted to press a piston (23) against the flexible wall (21) thereby releasing the substance from the reservoir (2) through an opening (25) in the reservoir (2). This provides for a safe and reliable medicament delivery device.
