A washing apparatus and a washing method, which further improve a washing effect and enable highly clean washing with a small amount of chemical. Also, it is an object of the invention to provide a washing apparatus of high throughput involving rapid switching of various chemicals of high responsibility and capable of performing a series of washing operations at high speed. The washing apparatus comprises undiluted cleaning liquid injection means for injecting an undiluted solution or undiluted gas of a cleaning liquid into a ultrapure water channel to make a cleaning liquid of a desired concentration, cleaning liquid supplying means connected to the super demineralized water channel for simultaneously supplying front and rear surface of a substrate with a cleaning liquid adjusted to a desired concentration or a ultrapure water, means for superposing ultrasonic wave or high frequency sound waves of 0.5 MHz or more on the substrate through the cleaning liquid, and means for rotating the substrate or means for moving either of the substrate and the cleaning liquid supplying means in one direction, whereby injection of the undiluted solution or undiluted gas into the ultrapure water channel is controlled to continuously perform washing of the substrate by the cleaning liquid and washing by the ultrapure water.