PURPOSE: To surely feed a mat seedling into an operation locus of a planting pawl by placing the mat seedling with an underlay and all on a seedling carrier and providing guide grooves engageable with protruding parts protruding from edges on both sides in the width direction of the underlay in a specific state in the seedling carrier.

CONSTITUTION: Protruding parts 11 protruding in the width direction are formed at a regular interval in the longitudinal direction in edges on both sides in the width direction of an underlay 2. Guide grooves for regulating a distance of the protruding parts separated from a seedling carrier 5 are installed in the seedling feeding direction in the seedling carrier. The protruding parts are engaged with the guide grooves and guided.