A slip determination system is provided that is capable of providing appropriate control information to a traveling vehicle when the traveling vehicle has proceeded to an area where a slip is likely to occur during automatic travel. The slip determination system includes: a vehicle position detection module for detecting a vehicle position; and an automatic travel control portion for enabling automatic travel based on the vehicle position and a set travel path; a slip amount calculation portion for calculating a slip amount of the traveling vehicle body, using an estimated movement distance of the traveling vehicle body calculated based on the number of revolutions of a driving axle of the traveling vehicle body, and an actual movement distance of the traveling vehicle body calculated based on the vehicle position; an appropriateness determination portion for performing appropriateness determination to determine, based on the slip amount, whether or not a state of a traveling ground surface is appropriate for automatic travel; and an automatic travel stop portion for stopping automatic travel based on a determination result.