An event analysis device having an event collector for collecting event log data representing an operation history by a DCS operator; an event analyzer for analyzing the event log data, and extracting basic unit operations or unit operations representing an operation method based on operations of the DCS operator or an operation intention based on operations of the DCS operator; an operation sequence extractor for extracting operation sequences which the basic unit operations or the unit operations are aligned in accordance with time order in every service time period; an operation clusterer for clustering the operation sequences based on similarity among the operation sequences extracted in every service time period; and an operation procedure generator for analyzing the operation sequences clustered in same type, and estimating a structure of the operation procedure based on the operation of the DCS operator.