A biosensor can supply a sample solution accurately and easily, and includes a capillary for collecting a sample solution and analyzes a specific substance in the sample solution, an air hole, and at least two supply ports, i.e., a sample supply port and an auxiliary sample supply port, so that supply of the sample solution can be performed from either of the supply ports. Even when the sample supply port is closed up with a fingertip or the like and supply of the sample solution is stopped, the sample solution can be quickly supplied from the other auxiliary sample supply port.