As insect olfaction is closely related to human society in many ways, it is of great interest to find its underlying process. Insects detect odorants through odorant receptors (ORs) that form channels with the common olfactory co-receptor (Orco) that is conserved among insects including fruit fly Drosophila melanogaster and is critical for the olfactory function. Although many aspects of insect olfaction have been revealed, it is not yet clear how exactly Orco is expressed and which genes in particular are related exclusively to the process. In this study, we generated a transcriptome of olfactory sensory neurons (OSNs) and profiled the changes in the genomic repertoire. By screening several candidates selected from the profile, we elucidated a novel transcription factor, CG7786. We validated CG7786 by checking the function and localization of ORs depending on the expression level of CG7786 and confirmed that it is involved in the expression of several ORs. CG7786 not only plays the critical role in the proper function of ORs under its control, but also is modulates the transcription of those ORs. The loss of OR expression in the CG7786 mutant background could be rescued by OR-specific expression of CG7786 both transcriptionally and functionally. This approach was sufficient to validate the effectiveness of transcriptomic approaches in search of novel genes related to Drosophila olfaction.