An injection device 200 for delivering a medicament from a syringe contained within a housing 201 of device 200. Device 200 is configured to move the syringe through the housing 201 to cause insertion of a needle 301 of the syringe into a user's skin and to subsequently move a bung 302 through a body 300 of the syringe to deliver medicament through the needle 301. Device 200 comprises: a plunger engaging the bung 302； a sleeve 208 located around the plunger； an insertion spring 206 biasing sleeve 208 relative to housing 201； and a delivery spring 207 biasing the plunger relative to sleeve 208. Device 200 further comprises: a mechanism for releasing the sleeve from the housing 201 to start insertion and after insertion for releasing the plunger from sleeve 208 to start delivery of the medicament； and a velocity regulator for regulating the plunger velocity upon its release from sleeve 208 and for disengaging from the plunger during delivery. The velocity regulator comprising a screw thread 209 associated with one of the sleeve 208 and the plunger and one or more thread engaging members formed on the other of the sleeve 208 and the plunger.
