The object of the present invention is to develop a technique for expressing a functional membrane-bound protein by using baculovirus and insect cell expression system. The present invention provides a method for expressing a functional membrane-bound receptor protein which comprises steps of culturing a host infected with at least one type of recombinant baculovirus which contains a gene encoding an interacting protein and a gene encoding a membrane-bound receptor protein which interacts with said interacting protein to perform its function, and co-expressing said interacting protein and said membrane-bound receptor protein in a budded baculovirus released from said host.