A substrate work system including a work device configured to perform predetermined work on a substrate by use of an exchangeable work unit (44, 50), the substrate work system comprising: a storage section configured to store the work unit (44, 50); a maintenance device (84, 87) configured to perform maintenance of the work unit (44, 50); a conveyance device capable of automatically conveying the work unit (44, 50), the conveyance device being an unmanned vehicle; and a determination section configured to determine a maintenance time for the work unit (44, 50) used in the work device based on quality information on work quality of the predetermined work, wherein the work device is a mounting device, the mounting device using, as the work unit (44, 50), a feeder configured to supply a component and a nozzle configured to pick up the component and configured to perform, as the predetermined work, mounting work of picking up the component supplied from the feeder with the nozzle and mounting the component so picked up on to the substrate, and wherein the determination section determines a maintenance time for the feeder and the nozzle based on state information on at least either of a suction state of the component and a mount state of the component as the quality information, characterized in that a control section (86, 89) is provided that is configured to, when the determination section determines that a maintenance time arrives, cause the conveyance device, the work device (30, 40), and the maintenance device (84, 87) to unload the work unit (44, 50) for exchange from the storage section, convey the work unit (44, 50) to the work device, for being exchanged with the work unit (44, 50) that has been used up in the work device, and convey the used-up work unit (44, 50) so exchanged to the maintenance device (84, 87) so as to be maintained thereby, the exchange and maintenance of the individual work units (44, 50) is automatic without involving exchange work and maintenance work by an operator, and the determination section determines whether an abnormality pre-indication state, which results before an abnormal state results, is present in at least either of the suction state and the mount state based on the state information, determines, when the component supplied from a specific feeder is in the abnormality pre-indication state, that a maintenance time arrives for the specific feeder, and determines, when the component picked up by a specific nozzle is in the abnormality pre-indication state, that a maintenance time arrives for the specific nozzle. a storage section configured to store the work unit (44, 50); a maintenance device (84, 87) configured to perform maintenance of the work unit (44, 50); a conveyance device capable of automatically conveying the work unit (44, 50), the conveyance device being an unmanned vehicle; and a determination section configured to determine a maintenance time for the work unit (44, 50) used in the work device based on quality information on work quality of the predetermined work, wherein the work device is a mounting device, the mounting device using, as the work unit (44, 50), a feeder configured to supply a component and a nozzle configured to pick up the component and configured to perform, as the predetermined work, mounting work of picking up the component supplied from the feeder with the nozzle and mounting the component so picked up on to the substrate, and wherein the determination section determines a maintenance time for the feeder and the nozzle based on state information on at least either of a suction state of the component and a mount state of the component as the quality information, characterized in that a control section (86, 89) is provided that is configured to, when the determination section determines that a maintenance time arrives, cause the conveyance device, the work device (30, 40), and the maintenance device (84, 87) to unload the work unit (44, 50) for exchange from the storage section, convey the work unit (44, 50) to the work device, for being exchanged with the work unit (44, 50) that has been used up in the work device, and convey the used-up work unit (44, 50) so exchanged to the maintenance device (84, 87) so as to be maintained thereby, the exchange and maintenance of the individual work units (44, 50) is automatic without involving exchange work and maintenance work by an operator, and the determination section determines whether an abnormality pre-indication state, which results before an abnormal state results, is present in at least either of the suction state and the mount state based on the state information, determines, when the component supplied from a specific feeder is in the abnormality pre-indication state, that a maintenance time arrives for the specific feeder, and determines, when the component picked up by a specific nozzle is in the abnormality pre-indication state, that a maintenance time arrives for the specific nozzle.