To make a liquid supply pump and a spray gun highly rigid, to reduce generation of pressure, to eliminate air bubbles in liquid, to form no air reservoir in a pipeline, and to certainly respond to a preliminarily programmed spray pattern since it is important to sufficiently consider influences of elastic displacement of components, and compression of liquid, etc. for the liquid supply pump and the spray gun in liquid spray with high accuracy, trace quantity, at slow speed, and with no pulsation.

The size of syringe capacity becomes proportional to a cross section when strokes are the same. In order to reduce a load of a syringe pump 1, the syringe capacity is made small to reduce the cross section. The syringe pump capable of performing an air bubble discharge operation, and a flow sensor 30 are adopted.