An apparatus for measuring substrate content present in a specimen that is applied to a biosensor comprising a working electrode, a counter electrode and a detecting electrode located on a first insulating support, the biosensor having a specimen supply path and a reagent layer for quantifying the substrate; the electrodes (5,6,7), the specimen supply path and the reagent layer existing between the first insulating support and a second insulation layer, the apparatus comprising: a first current/voltage conversion circuit for converting a current from the detecting electrode included in the biosensor into a voltage; a second current/voltage conversion circuit for converting a current from the working electrode included in the biosensor into a voltage; a first A/D conversion circuit for digitally converting the voltage from the first current/voltage conversion circuit; a second A/D conversion circuit for digitally converting the voltage from the second current/voltage conversion circuit; a first selector switch for switching the connection of the detecting electrode of the biosensor to the first current/voltage conversion circuit or the ground; and a control part for controlling the first A/D conversion circuit, the second A/D conversion circuit, and the first selector switch; and wherein the control part is configured to apply voltage between the detecting electrode and the counter electrode as well as between the working electrode and the counter electrode in a state where the first selector switch is connected to the first current/voltage conversion circuit, detect an electrical change between the detecting electrode and the counter electrode as well as an electrical change between the working electrode and the counter electrode, respectively, occurring by the sample liquid which is supplied to the reagent layer provided on the specimen supply path, thereafter connect the first selector switch to the ground, apply a voltage between the working electrode and the counter electrode as well as the detecting electrode, and measure a response current generated by applying the voltage, and prevent it from measuring the substrate content included in the specimen when it determines that the specimen has not been sufficiently supplied to the biosensor, even if additional specimen is thereafter added to the biosensor. a first current/voltage conversion circuit for converting a current from the detecting electrode included in the biosensor into a voltage; a second current/voltage conversion circuit for converting a current from the working electrode included in the biosensor into a voltage; a first A/D conversion circuit for digitally converting the voltage from the first current/voltage conversion circuit; a second A/D conversion circuit for digitally converting the voltage from the second current/voltage conversion circuit; a first selector switch for switching the connection of the detecting electrode of the biosensor to the first current/voltage conversion circuit or the ground; and a control part for controlling the first A/D conversion circuit, the second A/D conversion circuit, and the first selector switch; and wherein the control part is configured to apply voltage between the detecting electrode and the counter electrode as well as between the working electrode and the counter electrode in a state where the first selector switch is connected to the first current/voltage conversion circuit, detect an electrical change between the detecting electrode and the counter electrode as well as an electrical change between the working electrode and the counter electrode, respectively, occurring by the sample liquid which is supplied to the reagent layer provided on the specimen supply path, thereafter connect the first selector switch to the ground, apply a voltage between the working electrode and the counter electrode as well as the detecting electrode, and measure a response current generated by applying the voltage, and prevent it from measuring the substrate content included in the specimen when it determines that the specimen has not been sufficiently supplied to the biosensor, even if additional specimen is thereafter added to the biosensor.