A hydrogen generator (100) includes: a reformer (1) configured to generate a hydrogen-containing gas using a raw material and steam; a water evaporator (4) configured to supply the steam to the reformer (1); a sealing device (10) provided on a passage located downstream of the reformer (1) and configured to block a gas in the passage from flowing to the atmosphere; and a depressurizer (3) provided on a passage located upstream of the reformer (1) and configured to release to the atmosphere, pressure in the hydrogen generator (100) which pressure is increased by water evaporation in the water evaporator (4) after the sealing device (10) is closed.