To surely determine a deteriorating state of fluid supply capacity of a fluid supply means with simple constitution.

In this capacity determining method of the fluid supply means in a fluid using apparatus, the fluid supply capacity of the fluid supply means 4 is detected on the basis of consumption of fluid in the fluid using apparatus 1 and an operation state of the supply means 4 of the fluid to the fluid using apparatus 1, and this detecting value is compared with an initial value of the fluid supply capacity of the fluid supply means 4 to determine the deteriorating state of the fluid supply capacity.