IMAGE FORMING APPARATUS

To provide an image forming apparatus adapted to prevent lowering of productivity by eliminating the arrival delay of a sheet at an image forming unit without a change of the sheet transport speed when changing over the source of paper supply.SOLUTION: An image forming apparatus includes a paper-supply unit, an image forming unit, a sheet transport unit, a decrease detecting unit and a control unit. The control unit sets a preparatory paper-supply unit to start a preparation for changing over the source of paper supply based on an output of the decrease detecting unit. The control unit sets, as to the preparatory paper-supply unit, a predicted number of remaining sheets that is a prediction value of a remaining amount of sheets. The control unit sets any one of the paper-supply units accommodating sheets of the same size as the preparatory paper-supply unit as a destination-of-changeover paper-supply unit. The control unit sets the number of changeover sheets. The control unit subtracts 1 from the predicted number of remaining sheets each time the preparatory paper-supply unit supplies a sheet. When the predicted number of remaining sheets of the preparatory paper-supply unit becomes the number of changeover sheets or smaller, the control unit causes the destination-of-changeover paper-supply unit to start a supply of sheets.SELECTED DRAWING: Figure 6 【課題】給紙元の切り替え時、用紙搬送速度を変えることなく、画像形成部への用紙の到達遅延をなくし、生産性の低下を防ぐ。【解決手段】画像形成装置は、給紙部、画像形成部、用紙搬送部、減少検知部、制御部を含む。制御部は、減少検知部の出力に基づき、給紙元の切り替え準備を開始すべき準備給紙部を設定する。制御部は、準備給紙部について、用紙の残量の予測値である予測残枚数を設定する。制御部は、準備給紙部と同じサイズの用紙を収容する給紙部のうち、何れか１つを切替先給紙部に設定する。制御部は切替枚数を設定する。制御部は、準備給紙部が用紙を給紙するごとに予測残枚数から１を減算する。準備給紙部の予測残枚数が切替枚数以下になった時点で、制御部は、切替先給紙部に用紙の給紙を開始させる。【選択図】図６