We introduce a task analysis system for enroute air traffic control based on ESDA (Exploratory Sequential Data Analysis). The system integrates and synchronizes data from enroute simulator then visualizes them in various ways, such as "illustration of flight route and instruction timing on map" and "state chart of aircraft under control". Data in this system consists of movie file of RDP radarscope, communication between controller and pilot, output from real-time instruction recording software and simulator log file which contains flight plan and position of aircraft and pilot's input. Example of controller's taskload analysis using this system is shown and the result is examined for taskload modeling.