A determination method includes: using a microchip, including a capillary flow path and a sample reservoir connected to the capillary flow path at an upstream side, to fill the capillary flow path with a first solution for electrophoresis, and supply the sample reservoir with a second solution containing an analyte; applying a voltage between the sample reservoir supplied with the second solution and the inside of the capillary flow path filled with the first solution, to move a component contained in the second solution in the capillary flow path and separate the component in the capillary flow path; optically detecting a value related to a component difference between the first solution and the second solution, other than a value related to the analyte, for the separated component; and determining whether the optical detection is favorable or poor by comparing the optically detected value with a predetermined threshold value.