To provide an apparatus and a method for treating a substrate, by which even any developed substrate regardless of a kind or the like can be rinsed excellently by supplying a sufficient amount of a rinsing liquid.

The developed substrate W is rinsed by mixing at a nozzle 31 the nitrogen gas to be supplied from a nitrogen gas supplying source with the liquid to be supplied from a liquid supplying source and supplying the mixture as the rinsing liquid K to the substrate W from the nozzle 31. The sufficient amount of the liquid K can be supplied to any substrate W when the substrate W is rinsed since the discharge amount from the nozzle 31 to the substrate W can be set arbitrarily. Since it is unnecessary to use a high-pressure pump, the equipment cost of this apparatus can be reduced. Since the installation space of the high-pressure pump is not necessary, the size of this apparatus can be made small as a whole.