A kind of injection device, including a shell include the syringe (24) of (101) to (104). The content of syringe (24) sees the shell at the middle part (102) of (14) by window. Window (14) is hidden in by slideable shutter (12). Slideable shutter (12) also biases internal syringe carrier by biasing spring (22). A kind of turnover needle cap is also disclosed, is initially used to cover the front end of the shell, and when removed, by needle shield (30) from needle (26). The cap be designed as it is turnover so that after use,It can overturn and reconnect to the shell to cover exposed needle.
