A fuel cell system and a starting method therefor are capable of setting a start-up mode which is appropriate to energy stored in a secondary battery so as to eliminate problems in starting the fuel cell system. The fuel cell system includes a fuel cell, a secondary battery which is electrically connected with the fuel cell, a secondary-battery charge-amount detection unit which detects an amount of charge in the secondary battery, and a memory which stores at least one threshold value for determining the start-up mode of the fuel cell system. Stored electric energy which corresponds to the amount of charge in the secondary battery is calculated, and a start-up mode of the fuel cell system is determined based on the electric energy stored in the secondary battery and the threshold value stored in the memory.