For the expression of a foreign gene, a virus is provided in which at least a part of a cysteine protease gene present on a genome of a baculovirus has been deleted or substituted by a marker gene. A process is also disclosed for the formation of the virus. A transfer vector for the deletion of a cysteine protease gene is also described. This transfer vector comprises a DNA fragment of a nuclear polyhedrosis virus genome, in which at least a part of a cysteine protease gene has been substituted by a marker gene, and a plasmid vector fragment. Also disclosed is a process for the production of an economic protein. This production process comprises inoculating a host insect with a gene recombination virus, said gene recombination virus having been obtained by deleting or substituting by a marker gene at least a part of a cysteine protease gene present on a genome of a baculovirus or a nuclear polyhedrosis virus; expressing an economic protein gene inserted downstream a polyhedral gene promoter, granulin gene promoter or p10 gene promoter of the gene recombination virus; and collecting the economic protein.