An arithmetic device and a control apparatus capable of executing a process according to an event occurring in one or more functional units connected through a communication circuit are provided. The arithmetic device configuring the control apparatus includes: a communication circuit for exchanging data with the functional units through the communication line; a processor for executing at least one of an arithmetic processing using data acquired from the functional units and a generation processing of data to be transmitted to the functional units; and a monitoring circuit connected to the communication circuit and the processor, and includes: a detection unit that detects an event occurring in the arithmetic device; a storage unit that stores a message associated with each event; and a start unit that gives an instruction to the communication circuit in accordance with the detected event to transmit a message associated with the detected event.