1. A sewing machine comprising: a sewing machine bed configured so that a workpiece cloth is placed thereon; a feed mechanism provided in the bed and configured to move the workpiece cloth in a predetermined direction; a needle bar configured to accept a needle; a needle bar mechanism configured to drive the needle bar upward and downward; a needle position detector configured to detect whether or not the needle occupies a needle-down position where the needle penetrates the workpiece cloth or a needle-up position where the needle is located above the workpiece cloth; a first imaging member provided on the bed and configured to image a first range of an underside of the workpiece cloth while the workpiece cloth is being moved by the feed mechanism; a second imaging member provided on the bed and configured to image a second range of the underside of the workpiece cloth while the workpiece cloth is being moved by the feed mechanism, the second range differing from the first range; an imaging control unit configured to control an imaging process so that the imaging process is executed by the first imaging unit and the second imaging unit when the needle is located at the needle-up position, based on a result of detection by the needle position detector and so that the imaging process is stopped by the first and second imaging units when the needle is located at the needle-down position, based on a result of detection by the needle position detector; an image synthesis unit configured to synthesize the images obtained by the first and second imaging units, thereby obtaining a synthesized image; and a display unit configured to display the synthesized image obtained by the image synthesis unit.