It is intended to develop and provide a technique of conveniently allowing a transgenic silkworm by itself and at an individual level to produce a recombinant protein having a mammalian-type sugar chain sialic acid attached thereto, without the need of a baculovirus expression system or oral and transdermal administration of sialic acid. An expression vector was developed which can induce the expression of a mammalian-type glycosylation-related gene group only in a silk gland such that the recombinant protein modified with the mammalian-type sugar chain has no adverse effect on the silkworm itself. A transgenic silkworm harboring the expression vector was prepared.
