The present invention provides a system for preventing an accident that minimizes the number of monitor devices and prevents a collision accident to reduce the work and cost burdens. The system for preventing an accident 1 of the present invention includes an imaging device 10, a monitor server 20, and a warning device 60. The control unit 30 of the monitor server 20 executes the area receiving module 31 to receive input of an approach area as an area where a vehicle approaches and a danger area where is danger from an approaching vehicle based on a base image taken by the imaging device 10. The control unit 30 executes the time period judgment module 33 to judge whether or not it is a time period when a vehicle enters the approach area. If a vehicle enters the approach area, the control unit 30 executes the second judgment module 35 to judge whether or not a person, etc., enters the approach area or the danger area. If a person, etc., enters the approach area or the danger area, the control unit 30 executes the warning module 36 to instruct the warning device 60 to provide warning information.