A ventilation system for a tank which stores water to be supplied to a fuel cell, which includes: a ventilator for ventilating the tank; a gas discharge line to guide gas in the tank to outside; a separator for separating moisture and/or water from the gas from the tank; a water discharge line to guide the water separated by the separator to outside; and an air supply line connected to the water discharge line, which is to supply air for vaporizing water from the water discharge line.