Provided is a microchip which is capable of determining the quantity of the liquid in the chip and dividing the liquid, and has a relatively simple flow passage structure. In the microchip liquid supply system, a portion of the liquid in an upstream passage among the liquid injected into a first flow passage is supplied from a liquid discharge passage by operating a suction pump connected to a liquid supply passage in such a state that an air vent hole is closed. Thereafter, the suction pump is operated with the air vent hole closed, whereby a portion of the liquid in a quantity determination passage among the liquid injected into the first flow passage is supplied from a liquid supply passage.