A board work system comprising: a conveying and holding device including a pair of rails (106, 108) configured to support a board, and a changing mechanism configured to change a distance between the pair of rails (106, 108), the conveying and holding device being configured to convey the board supported by the rails (106, 108) and hold the board at a work position; a work device configured to perform work with respect to the board held by the conveying and holding device from an underside of the board; a moving device configured to move the work device and including an X-direction moving device, and a Y-direction moving device, wherein the X-direction and the Y-direction are directions in the width direction and the front rear direction of the work device; and a control device, the control device including an acquiring section configured to acquire a rail spacing distance that is the distance between the pair of rails (106, 108), and an operation control section configured to control operation of the moving device based on the rail spacing distance acquired by the acquiring section, characterized in that: the control device is configured to calculate a movement range of the work device based on the rail spacing distance during mounting work considering the external dimensions of the work device, the internal dimensions of the board conveying and holding device, and clearance between the board conveying and holding device and the work device, wherein the operation of the unit moving device is controlled such that the work device is not moved to exceed beyond the movement range so as to prevent interference between the work device and the conveying and holding device. a conveying and holding device including a pair of rails (106, 108) configured to support a board, and a changing mechanism configured to change a distance between the pair of rails (106, 108), the conveying and holding device being configured to convey the board supported by the rails (106, 108) and hold the board at a work position; a work device configured to perform work with respect to the board held by the conveying and holding device from an underside of the board; a moving device configured to move the work device and including an X-direction moving device, and a Y-direction moving device, wherein the X-direction and the Y-direction are directions in the width direction and the front rear direction of the work device; and a control device, the control device including an acquiring section configured to acquire a rail spacing distance that is the distance between the pair of rails (106, 108), and an operation control section configured to control operation of the moving device based on the rail spacing distance acquired by the acquiring section, characterized in that: the control device is configured to calculate a movement range of the work device based on the rail spacing distance during mounting work considering the external dimensions of the work device, the internal dimensions of the board conveying and holding device, and clearance between the board conveying and holding device and the work device, wherein the operation of the unit moving device is controlled such that the work device is not moved to exceed beyond the movement range so as to prevent interference between the work device and the conveying and holding device.