An injection device adapted for adhering to skin of a user to inject a liquid into the user includes an adhesive patch, and an injection module. The adhesive patch has a patch body and a hollow region that is formed in the patch body. The patch body has opposite first and second surfaces, the second surface being adapted for adhering to the skin of the user. The injection module includes a connecting seat and a catheter connected to the connecting seat and having a secured end portion and an injection end portion that is opposite to the secured end portion. The catheter extends, at an angle to the adhesive patch, from the connecting seat through the hollow region to a side of the adhesive patch corresponding to the second surface.
