1. A water content estimation apparatus, comprising: a first detection unit for detecting a first information regarding a water content of a sheet material at a position in contact with or adjacent to the sheet material; a second detection unit for detecting a second information regarding at least one of factors that change the water content of the sheet material from conveyance of the sheet material detected by the first detection unit until a performance of a processing, results of the processing being affected by the water content of the sheet material; and an estimation computation unit for computing, based on the detection results obtained by the first detection unit and the second detection unit, an estimation of the water content of the sheet material when the processing is performed with respect to the sheet material.