A mixer control device having a function of a monitoring device acquires measurement data of monitoring target information that is obtained through measurement when a rubber material is kneaded by a mixer. In addition, the mixer control device compares the measurement data and reference data that is selected in past measurement data of the monitoring target information and performs abnormality determination. The mixer control device acquires measurement data that is measured from predetermined mixing operation initiation timing in a series of mixing operations of a rubber material in the mixer for every unit of the series of mixing operation.