A method of measuring a quantity of a substrate included in sample liquid, comprising the steps of: providing a biosensor which includes: an insulating board; an electrode section formed on at least a part of the insulating board, the electrode section including a counter electrode, a measuring electrode, and a detecting electrode; a sample supplying path for supplying the sample liquid to the electrode section; and a reagent layer for reacting with the sample liquid supplied through the sample supplying path, wherein an air hole is provided more downstream than the detecting electrode for accelerating the flow of the sample liquid; providing a measuring device which includes: a supporting section for detachably supporting the biosensor; and a connecting terminal and a driving power supply for applying a voltage to the electrode section; inserting the biosensor into the supporting section of the measuring device; and applying a voltage with the driving power supply to a first group including the counter electrode and the measuring electrode; applying a voltage with the driving power supply to a second group including the detecting electrode and one of the measuring electrode and the counter electrode; and determining that the sample liquid is sucked from the air hole by mistake when the electric current from the second group exceeds a predetermined threshold before the electric current from the first group exceeds a predetermined threshold and when the electric current from the first group does not exceed the predetermined threshold within a given lapse of time. providing a biosensor which includes: an insulating board; an electrode section formed on at least a part of the insulating board, the electrode section including a counter electrode, a measuring electrode, and a detecting electrode; a sample supplying path for supplying the sample liquid to the electrode section; and a reagent layer for reacting with the sample liquid supplied through the sample supplying path, wherein an air hole is provided more downstream than the detecting electrode for accelerating the flow of the sample liquid; an insulating board; an electrode section formed on at least a part of the insulating board, the electrode section including a counter electrode, a measuring electrode, and a detecting electrode; a sample supplying path for supplying the sample liquid to the electrode section; and a reagent layer for reacting with the sample liquid supplied through the sample supplying path, wherein an air hole is provided more downstream than the detecting electrode for accelerating the flow of the sample liquid; providing a measuring device which includes: a supporting section for detachably supporting the biosensor; and a connecting terminal and a driving power supply for applying a voltage to the electrode section; a supporting section for detachably supporting the biosensor; and a connecting terminal and a driving power supply for applying a voltage to the electrode section; inserting the biosensor into the supporting section of the measuring device; and applying a voltage with the driving power supply to a first group including the counter electrode and the measuring electrode; applying a voltage with the driving power supply to a second group including the detecting electrode and one of the measuring electrode and the counter electrode; and determining that the sample liquid is sucked from the air hole by mistake when the electric current from the second group exceeds a predetermined threshold before the electric current from the first group exceeds a predetermined threshold and when the electric current from the first group does not exceed the predetermined threshold within a given lapse of time.