Abstract: Infusion apparatus is provided for discriminating the specifications of syringes of any manufacturer, setting alarm levels corresponding to contained liquid solutions having various viscosities, and obtaining a net pressure for infusion from the force to a plunger by considering pressure loss dependent on a friction factor between the barrel and the plunger of the syringe. Syringe diameter is detected digitally to determine a capacity signal. The plunger force is detected by a pressure sensor and then A/D converted to a digital pressure signal. Specifications of syringes of manufacturers based on the syringe capacity signal are compared with the signals of the mounted syringe to select one among operation programs corresponding to their syringe specifications. A Dip switch selects a group of the operation programs for manufacturers.