The present invention provides a vector containing a DNA construct containing a first promoter that is a nitrilase gene promoter, a multicloning site and a nitrilase transcription regulatory protein gene (particularly preferably a structural gene is ligated into a multicloning site and a second promoter is placed at the upstream of the nitrilase transcription regulatory protein gene), and the like. The present invention affords a high expression system capable of expressing a large amount of useful proteins by actinomycete host represented by actinomycete belonging to the genus Streptomyces and the like beneficially used for the production of useful proteins.