A microfluidic device for amplifying a nucleic acid, comprising: a cartridge configured to store a solution containing the nucleic acid; a light source; a light receiving sensor; and a control part controlling the cartridge, the light source and the light receiving sensor, wherein the cartridge comprises: a tank part storing the solution; a plurality of first chambers holding the solution from the tank part; a plurality of first heaters corresponding to the first chambers; and a plurality of flow path parts connecting the tank part and the first chambers, wherein each of the first chambers comprises: a first opening connected to the flow path part; and a second opening for discharging the solution held in the first chamber, the light source is configured to irradiate light to the first chambers, the light receiving sensor is configured to measure a fluorescence intensity of each of the first chambers, and the control part is configured to: control execution of a thermal cycle which changes a temperature of the first chambers, count a number of repetitions of the thermal cycle for each of the first chambers and store a count value, acquire from the light receiving sensor the fluorescence intensity of each of the first chambers for each thermal cycle, determine whether the acquired fluorescence intensity of each of the first chambers is within a predetermined range defined in advance for each number of repetitions, and determine the first chamber to be a defective chamber when it is determined that the fluorescence intensity is not within the predetermined range, and the microfluid device being characterized in that: the control part is further configured to reset the count value of the defective chamber, discharge the solution from the defective chamber, and fill the defective chamber with a new solution from the tank part. a cartridge configured to store a solution containing the nucleic acid; a light source; a light receiving sensor; and a control part controlling the cartridge, the light source and the light receiving sensor, wherein the cartridge comprises: a tank part storing the solution; a plurality of first chambers holding the solution from the tank part; a plurality of first heaters corresponding to the first chambers; and a plurality of flow path parts connecting the tank part and the first chambers, wherein each of the first chambers comprises: a first opening connected to the flow path part; and a second opening for discharging the solution held in the first chamber, a tank part storing the solution; a plurality of first chambers holding the solution from the tank part; a plurality of first heaters corresponding to the first chambers; and a plurality of flow path parts connecting the tank part and the first chambers, wherein each of the first chambers comprises: a first opening connected to the flow path part; and a second opening for discharging the solution held in the first chamber, a first opening connected to the flow path part; and a second opening for discharging the solution held in the first chamber, the light source is configured to irradiate light to the first chambers, the light receiving sensor is configured to measure a fluorescence intensity of each of the first chambers, and the control part is configured to: control execution of a thermal cycle which changes a temperature of the first chambers, count a number of repetitions of the thermal cycle for each of the first chambers and store a count value, acquire from the light receiving sensor the fluorescence intensity of each of the first chambers for each thermal cycle, determine whether the acquired fluorescence intensity of each of the first chambers is within a predetermined range defined in advance for each number of repetitions, and determine the first chamber to be a defective chamber when it is determined that the fluorescence intensity is not within the predetermined range, and control execution of a thermal cycle which changes a temperature of the first chambers, count a number of repetitions of the thermal cycle for each of the first chambers and store a count value, acquire from the light receiving sensor the fluorescence intensity of each of the first chambers for each thermal cycle, determine whether the acquired fluorescence intensity of each of the first chambers is within a predetermined range defined in advance for each number of repetitions, and determine the first chamber to be a defective chamber when it is determined that the fluorescence intensity is not within the predetermined range, and the microfluid device being characterized in that: the control part is further configured to reset the count value of the defective chamber, discharge the solution from the defective chamber, and fill the defective chamber with a new solution from the tank part.