A fuel reformer including a reaction container including a first chamber, a first reactor in the first chamber, the first reactor, including a first catalyst, being configured to produce a first reformate by performing a steam reforming reaction on a first fuel, and having a first gas hourly space velocity (GHSV) at a set flow rate, a first heat source thermally connected to the first reactor, and a second reactor connected to the first reactor, the second reactor including a second catalyst, being configured to produce a second reformate having a lower carbon monoxide content than the first reformate, and having a second GHSV greater than the first GHSV at the set flow rate.