An injection syringe including a device for preparation of an injection in situ, useful to the injection which is liable to suffer chemical changes if left for a long time in the state of solution or dispersion ready to inject. The injection syringe is portable by a patient who may prepare a necessary injection in situ with the use of a device included in the syringe which will automatically perform an injection with a prescribed dosage. The injection syringe includes a device for preparation of an injection, whereby mechanical impacts affecting the medicine and consequently, chemical changes with a medicine would be minimized during the step of dissolving the medicine. The syringe as noted is especially useful for preparation of injection and injection of human growth hormones, interferon and various polypeptides which are of an environmentally sensitive nature and liable to suffer chemical changes if left for a long time in the state of solution or dispersion.