According to an embodiment, there is provided a substrate holder including: a first holding member; a second holding member; a clamper configured to clamp the first holding member and the second holding member; and a seal including a contact portion configured to contact at least one of the first holding member, the second holding member, and a substrate when the first holding member and the second holding member are clamped, in which the contact portion includes, in cross-section viewed in a plane passing a center of the substrate and perpendicular to a surface of the substrate, a first arc portion centered on a first point and a second arc portion centered on a second point different from the first point, and at least one of the first arc portion and the second arc portion has a curvature radius of 0.01 mm to 0.1 mm.