Abstract: A gas shortage preventive circuit for use in a fuel cell power generation circuit that includes a fuel cell, an inverter, and a constant voltage controlling circuit. The gas shortage preventive unit cooperates with an overcurrent limiting unit. The gas shortage preventive unit has an allowable overcurrent value calculating portion which calculates an allowable overcurrent value based on a fuel utilization coefficient which is higher by a certain proportion higher than a standard value and the output current of the fuel cell. The gas shortage preventive unit also has a response speed controlling portion which eliminates transient variations from the allowable overcurrent value and outputs an overcurrent value signal. The overcurrent limiting unit outputs to the constant volume controlling circuit a signal for suppressing an overcurrent when the output current of the fuel cell exceeds the preset overcurrent value.