The role of the conserved sequence region III in the promoter regions of the amylase-encoding genes amyB, glaA and agdA of Aspergillus oryzae was examined. Introduction of multiple copies of the region III fragment into the agdA promoter resulted in a significant increase in promoter activity at the transcriptional level. This result suggests that the fragment comprising region III consists of one or more cis-acting sequence(s). Moreover, expression of the agdA gene under the control of the improved agdA promoter resulted in efficient overproduction of α-glucosidase, even in the presence of glucose. Thus, overexpression of genes controlled by the improved promoter incorporating region III is possible. Interestingly, expression of the amyB and glaA genes in the transformant was strongly repressed. This result suggests that the trans-acting regulatory protein(s) that interact with region III are common to these amylase genes and that the titration of regulatory protein(s) reduced the expression of the amyB and glaA genes.