A first light emitter emits light toward a sheet. A first light receiver receives first reflected light from the sheet. A second light emitter is arranged downstream of the first light emitter in a conveyance direction of the sheet and emits light toward the sheet. A second light receiver receives second reflected light from the sheet. A measuring section measures first and second received light quantities of the first reflected light and the second reflected light. A moisture content calculator calculates a change in a moisture content of the ink in the sheet based on a difference between first and second moisture contents. The first moisture content is based on the first received light quantity and the second moisture content is based on the second received light quantity. A curling amount calculator calculates a curling amount of the sheet based on the change in the moisture content.