Abstract: The substrate treatment apparatus includes a substrate holder mechanism for holding a substrate to be treated, and a bifluid nozzle for supplying liquid droplets on a surface of the substrate held by the substrate holder mechanism. The bifluid nozzle has a casing, a liquid outlet port for discharging a treatment liquid, and gas outlet port for discharging a gas, and is adapted to introduce the treatment liquid and the gas into the casing, to generate droplets of the treatment liquid by mixing the treatment liquid discharged from the liquid outlet port with the gas discharged from the gas outlet port outside the casing, and to supply the liquid droplets on the substrate. The density of the liquid droplets supplied from the bifluid nozzle on the substrate surface is not less than 108 droplets/m2 per minute.