Provided is an agent for preventing an anxiety-related behavior in a growing stage attributable to a stress in infancy via ingestion by an infant who receives the stress in infancy. Also provided is an agent for preventing an anxiety-related behavior in a growing stage attributable to a stress in infancy comprising a lactoferrin and/or a lactoferrin degradation product as active ingredient or a food composition for preventing an anxiety-related behavior in a growing stage attributable to a stress in infancy comprising a lactoferrin and/or a lactoferrin degradation product as active ingredient characterized in that the lactoferrin and/or the lactoferrin degradation product is used via ingestion during infancy for a normal infant at birth and receives the stress in infancy.
