Abstract: An object of the present disclosure is to provide a technique for improving fluorescence detection accuracy in biological sample analysis. The present disclosure provides a back-illuminated imaging element including a plurality of pixel units, each of which includes at least an analyte holding unit configured to hold an analyte and a fluorescence detection unit that detects fluorescence generated by irradiating the analyte with excitation light. In addition, the present disclosure also provides a flow channel unit for analyzing a biological sample including the back-illuminated imaging element. In addition, the present disclosure also provides a biological sample analysis system that analyzes a biological sample using the flow channel unit for analyzing a biological sample.