NOVELTY - Fuel reformer contains modifier comprising catalyst layer into which water, natural gas and methanol are supplied with oxygen or air and hydrogen rich reformed gas is formed. The reformer is provided with O2 and raw material supply systems for respectively supplying O2 or air and raw material to modifier. A part of reformed gas is recirculated to modification catalyst layer through recycling pipe (71).    USE - For supplying hydrogen rich fuel to fuel cell power generating device.    ADVANTAGE - Oxidation of catalyst at inlet portion of modification catalyst layer is prevented. Stability and durability of the apparatus are improved.    DETAILED DESCRIPTION - Fuel reformer contains a modifier (5) comprising modification catalyst layer into which hydrocarbon fuel such as natural gas and methanol are supplied along with oxygen or air, and hydrogen rich reformed gas is formed by partial oxidation reaction and water vapor modification reaction. The oxygen supply system (60) is provided for supplying oxygen or air to modifier and raw material supply system (50) is provided for supplying raw material to the modifier. A part of reformed gas is recirculated to modification catalyst layer through recycling pipe (71). INDEPENDENT CLAIMS are also included for the following: (i) fuel cell power generating device equipped with modifier which supplies reformed gas to fuel cell main body, raw material supply system for supplying raw material to modifier, oxygen supply system for supplying oxygen or air to the modifier and recirculating pipe for recirculating a part of OFF hydrogen ejected from part of the fuel cell main body or modification catalyst layer of modifier; and (ii) starting method of reformer which involves detecting amount of raw material supplied to the modifier during initiation of modification process and supplying oxygen or air to the modifier from oxygen supply system.    DESCRIPTION OF DRAWING(S) - The figure shows the example of a fuel reformer.    Modifier (5)    Raw material supply system (50)    Oxygen supply system (60)    Reformed gas recycling pipe (71)