To provide a heterologous protein expression system which enables the fission yeast Schizosaccharomyces pombe as a host to produce of a heterologous protein which is almost impossible to express, or if possible, produced at low levels, under control of conventional promoters.The present invention provides an expression for use in the fission yeast Schizosaccharomyces pombe, a transformant carrying the expression vector, a method for producing a heterologous protein using the transformant, in particular a method for producing a heterologous protein in which a heat shock protein gene promoter in Schizosaccharomyces pombe is used to regulate gene expression by application of a specific form of stress, whereby the timing of the production of the desired heterologous protein can be controlled.