An apparatus for the self-dosing of a liquid medicine. The apparatus includes a chamber formed in a casing for receiving a liquid medicine to be self-dosed by a patient, with an inlet and outlet port formed to communicate with the chamber free from leakage of the medicine. The apparatus further includes a piston fitted liquid-tightly in the chamber, a push button attached to and adapted to actuate the piston and which is capable of being pressed by the patient a desired number of times corresponding to an amount of liquid medicine to be dosed, and a spring urging the piston towards its home position. After the patient presses the button and removes his hand from the button, the spring forces the piston backwards to its home position and the resulting negative pressure causes a subsequent smooth refilling of the chamber. The apparatus, which is a simple structure and can be manufactured at a low cost, can be employed in an integrated system for the self-dosing of the liquid medicine.