An image retrieval assist device that is communicably connected to an investigation assist device for recording captured images of cameras installed at a plurality of intersections respectively in correlation with camera information and intersection information. The image retrieval assist device has a processor, a communication unit; and a storage that stores an extraction condition of an image for each type of event that has occurred at the intersection, the image indicating a situation at a time of occurrence of the event. The processor accepts an input of event information including the type of event. The processor generates an image retrieval key including the extraction condition according to the input event information. The communication unit transmits the generated image retrieval key to the investigation assist device.