1. A non-transitory computer-readable recording medium having stored therein a program that causes a computer to execute a process comprising: calculating, for each of a plurality of grids through which a track of a specific vessel passes, an angle of approach and an angle of exit of the track, respectively; extracting a grid for which the angle of approach and the angle of exit conform to a determining condition set for each of the grids based on the determining condition; and determining whether the specific vessel has taken an avoidance behavior based on a relative distance from another vessel corresponding to a position of the specific vessel in a track in the extracted grid.