An auto-injector apparatus includes a flexible container containing a liquid medicant, a needle communicated with a container, a housing with a container being received in the housing, a pump disposed in the housing and positioned to engage the flexible container and expel the medicant from the container through the needle upon relative movement between the pump and the container, and a main drive spring operably associated with the needle to extend the needle from a first needle position wherein the needle is completely received in the housing to a second needle position wherein the needle protrudes from the housing. The pump may be a roller.