The copy machine selects either of a first direction in which a long-side direction of the paper matches the writing sub-scan direction and a second direction in which a short-side direction of the paper matches the writing sub-scan direction, with considering, when the paper is fed in the first direction, the number of documents, the number of copies, the time required for a reading process, the time required for an image forming process, and the time the reading process and the image forming process overlap, and with considering, when the paper is fed in the second direction, the number of documents, the number of copies, the time required for the reading process, the time required for a rotation process, and the time required for an image forming process.