In this invention, a high-voltage generation unit (100) comprises a unit casing, a discharge unit, and a protruding section. The protruding section is disposed downward from the discharge unit, and protrudes from the unit casing to a greater extent than the discharge unit. A holder holds the high-voltage generation unit in an attachable/detachable manner. A holder housing section (130) can receive the attachment of the holder. A holder passage, through which the holder passes when being attached to the holder housing section (130), is formed in the holder housing section (130). An opening section (132) at which the holder passage communicates with the exterior is formed in the holder housing section (130). The bottom wall surface of the holder passage comprises a planar opening section bottom surface (136) continuous to the opening section (132) and a step (137) extending downward relative to the height of the opening section bottom surface (136).