An event information memory for storing event information and an event management information memory for storing event management information are provided. The event information contains an event and an event execution time defined in advance as time from start of the event to its end. The event management information contains executing event related information on an executing event and a maximal allowed time that is allowed as the maximum of a total time of a remaining time of each executing event. The executing event related information is updated in accordance with an elapse of time. A display device is caused to display an event progress status graph on a display screen of the display device on the basis of the event management information. The event progress status graph indicates a status of the remaining time of each executing event in the maximal allowed time.