A system comprising a slave device (3a, 3b, 3c) including a control device configured to control an operation of the slave device (3a, 3b, 3c), which slave device (3a, 3b, 3c) is configured to be connected to a master device via an EtherCAT, and configured to be connected to a control target device, said control device comprising: a slave communication controller configured to control communication carried out via the EtherCAT; a processing section configured to carry out arithmetic processing; an operation monitoring section configured to monitor an operation of the control device; and the slave device (3a, 3b, 3c) further comprising an output section configured to supply a control signal to the control target device whose operation is controlled in accordance with a command transmitted from the control device, the slave communication controller, the processing section, and the operation monitoring section being configured as a one-chip integrated circuit, the operation monitoring section including a watchdog timer, a during-malfunction operation control section configured to control a during-malfunction operation in a case where the malfunction has occurred in the operation of the control device, and an interrupt controller, the control device being configured so that in a case where the watchdog timer has detected that the malfunction has occurred in the operation of the control device, the watchdog timer transmits, to the during-malfunction operation control section, a malfunction occurrence signal indicating that a watchdog timeout has occurred, and the control device being configured so that in a case where the during-malfunction operation control section has received the malfunction occurrence signal, (i) the during-malfunction operation control section causes the interrupt controller to carry out an interrupt procedure so as to reset the processing section and (ii) the during-malfunction operation control section carries out control to (a) cause the interrupt controller to allow for continuation of communication between the master device and the slave device (3a, 3b, 3c) and (b) block the output section from supplying the control signal to the control target device. a slave communication controller configured to control communication carried out via the EtherCAT; a processing section configured to carry out arithmetic processing; an operation monitoring section configured to monitor an operation of the control device; and the slave device (3a, 3b, 3c) further comprising an output section configured to supply a control signal to the control target device whose operation is controlled in accordance with a command transmitted from the control device, the slave communication controller, the processing section, and the operation monitoring section being configured as a one-chip integrated circuit, the operation monitoring section including a watchdog timer, a during-malfunction operation control section configured to control a during-malfunction operation in a case where the malfunction has occurred in the operation of the control device, and an interrupt controller, a watchdog timer, a during-malfunction operation control section configured to control a during-malfunction operation in a case where the malfunction has occurred in the operation of the control device, and an interrupt controller, the control device being configured so that in a case where the watchdog timer has detected that the malfunction has occurred in the operation of the control device, the watchdog timer transmits, to the during-malfunction operation control section, a malfunction occurrence signal indicating that a watchdog timeout has occurred, and the control device being configured so that in a case where the during-malfunction operation control section has received the malfunction occurrence signal, (i) the during-malfunction operation control section causes the interrupt controller to carry out an interrupt procedure so as to reset the processing section and (ii) the during-malfunction operation control section carries out control to (a) cause the interrupt controller to allow for continuation of communication between the master device and the slave device (3a, 3b, 3c) and (b) block the output section from supplying the control signal to the control target device.