A substrate holder has two holder constituting bodies, each having a plurality of columns arranged on an imaginary circle, and substrate holding sections that hold circumferential portions of respective substrates. The holder constituting bodies hold the substrates so that either their front surfaces or their back surfaces face upward with a substrate having an upward facing front and a substrate having an upward facing rear being alternately arranged in a vertical direction. At least one of the holder constituting bodies moves in the vertical direction to change the positions of the holder constituting bodies relative to each other. A distance between a first pair of vertically adjacent substrates with their respective front surfaces facing each other is set to ensure treatment uniformity, and to be larger than a distance between a second pair of vertically adjacent substrates with their respective back surfaces facing each other.