To provide a biosensor including a suctioning mechanism while using a detection element such as a surface acoustic wave device, included are: a first cover member 1 including an element-accommodating recess 5 on an upper face thereof; a detection element 3 including an element substrate 10, and at least one detection unit 13 located on the upper face of the element substrate 10 to perform detection of an analyte; and a second cover member 2 joined to the first cover member 1 and covering the detection element 3, and including an inflow port 14 from which the analyte flows in and a groove 15 extending from the inflow port 14 to at least above the detection unit.