An excavation control system includes a working unit having a bucket, a designed landform data storage part storing designed landform data, a bucket position data generation part that generates bucket position data, a designed surface data generation part, and an excavation limit control part. The designed surface data generation part generates superior and subordinate designed surface data based on the designed landform and bucket position data. The superior designed surface data indicates a superior designed surface corresponding to a prescribed position on the bucket. The subordinate designed surface data indicates a plurality of subordinate designed surfaces linked to the superior designed surface. The designed surface data generation part generates shape data based on the superior and subordinate designed surface data. The shape data indicates shapes of the superior designed surface and the plurality of subordinate designed surfaces. The excavation limit control part automatically adjusts position of the bucket.