An event analyzing device connectable to a historian which stores a log of a plurality of pieces of event data and a log of process data, the event data representing an event including an alarm which has occurred in a plurality of devices in a plant and an operation performed to the devices, the process data being of the devices in the plant, the event analyzing device comprising: an event data collector configured to collect the event data from the historian; a process data collector configured to collect the process data from the historian; a trend change detector configured to detect a trend change representing a change of a trend of the process data collected by the process data collector; an event data converter configured to convert the process data into process variation event data having information representing start time and end time of a continuation period of the trend change detected by the trend change detector; characterized by an event data aggregator configured to aggregate the plurality of pieces of the event data of a same kind collected by the event data collector to generate continued event data having information representing start time and end time of a continuation period of the event; and a cause-effect relationship analyzer configured to generate a cause-effect model using integrated event data in which the continued event data generated by the event data aggregator is integrated with the process variation event data converted by the event data converter, the cause-effect model being used for analyzing a cause-effect relationship between the event and a process change event, wherein the cause-effect relationship analyzer comprises a cause-effect model building module configured to build a Bayesian network in which the cause-effect relationship is represented in terms of probabilities in the cause-effect model. an event data collector configured to collect the event data from the historian; a process data collector configured to collect the process data from the historian; a trend change detector configured to detect a trend change representing a change of a trend of the process data collected by the process data collector; an event data converter configured to convert the process data into process variation event data having information representing start time and end time of a continuation period of the trend change detected by the trend change detector; characterized by an event data aggregator configured to aggregate the plurality of pieces of the event data of a same kind collected by the event data collector to generate continued event data having information representing start time and end time of a continuation period of the event; and a cause-effect relationship analyzer configured to generate a cause-effect model using integrated event data in which the continued event data generated by the event data aggregator is integrated with the process variation event data converted by the event data converter, the cause-effect model being used for analyzing a cause-effect relationship between the event and a process change event, wherein the cause-effect relationship analyzer comprises a cause-effect model building module configured to build a Bayesian network in which the cause-effect relationship is represented in terms of probabilities in the cause-effect model.