A method of detecting degradation of a membrane electrode assembly of a fuel cell is provided. In the method, it is possible to detect degradation (cross leakage) of the fuel cell. In the measurement step, the pressure drop value of the pressure of the fuel gas which decreases in the power generation state after discharging of the predetermined amount of the fuel gas, in each predetermined period of time is measured a plurality of times. Thereafter, in the determination step, it is determined that the membrane electrode assembly has been degraded in the case where the minimum pressure drop value, among a plurality of pressure measurement values, exceeds a threshold value.