A fuel cell system and a starting method therefore prevent problems when the system is started. The fuel cell system includes a fuel cell, a secondary battery that is electrically connected with the fuel cell, and a cell temperature sensor that detects a temperature of the fuel cell. Energy which is necessary for starting the fuel cell system is calculated based on the temperature of the fuel cell detected by the cell temperature sensor. The calculated value is used as a threshold for determining a start-up mode of the fuel cell system.