In biosensor system 1, biosensor 2 is mounted in measuring apparatus 3 for quantifying or detecting existence of a targeted substrate in a sample solution. Mounting end portion 20 of biosensor 2 to be mounted in measuring apparatus 3 has an extension of one base plate in the length direction, and further extensions of the other base plate in the width direction. Sensor mounting portion 30 of measuring apparatus 3 has a shape matching up with the shape of mounting end portion 20. Thereby wrong insertion of biosensor 2 in measuring apparatus 3 can be prevented. Further, varying shapes of plural biosensors 5 and 6 to have a common part and a non-common part, such biosensors can be handily measured by one measuring apparatus 7.