The theories of external information search reviewed in the respects of cost-benefit approach and psychological motivation approach are integrated to have more explaining power on the external information search behavior because of the relationships between two approaches. From the empirical research we get the results that motivation, search benefits and prior product knowledge have the direct effect on the extent of external information search but the search coat not. On the other hand, it was verified that cost and benefits, need for cognition, prior product knowledge, and prepurchase involvement have direct effects on the search motivation. And the direct effects of the fitness of internal information and the brand similarities on the search benefits and the direct effects of positive experience and prepurchase involovement on the search cost are verified through the experirmental research.