Background: In general, solid oxide fuel cell (SOFC) systems are said to be flexible to various kind of fuels such as natural gas and petroleum gas. The fuels are reformed at a reformer and supplied to anode. Cell testing for 10 to 100 W-class SOFCs needs steady supply of a real reformate gas or a simulated reformate gas. However, it is difficult to reform heavier hydrocarbons without know-how and to evaporate small flow-rate of water. In addition, cell performance comparison with reformate gases of various fuels has been scarcely reported. Method of approach: A new testing system, what we call “simulated-reformate-gas generator” was developed to simulate reformate gases from H2 , O2 , and CO2 stably and safely without dealing with toxic CO. An anode-supported planar Ni-YSZ/YSZ/LSCF cell (100 cm2 ) was subjected to voltage-current density (V-J) characteristic to discuss validity of the generator and to evaluate fuel flexibility with practical size of the cell. Results: It was clarified that equilibrium compositions at steam reforming of hydrocarbons and oxygen-containing biodiesel (C17 H33 COOCH3 ) can be simulated with ±1.0 mol.% precision by the generator. It was found that anode gas conditions can change quickly to shorten voltage stabilizing time at testing. Furthermore, it was elucidated that V-J characteristics hardly changed for simulated reformate of CH4 , C3 H8 , kerosene (C12 H24 ), and biodiesel at S/C = 3.0. DC electrical efficiency was estimated for the fuels as 54.2, 52.9, 52.5, 52.3% (LHV), respectively.Conclusions: The developed simulated-reformate-gas generator is so precise and useful for cell testing, making it easy to change anode gas conditions. As long as fuels for SOFC systems are reformed to thermodynamic equilibrium, cell performance and electrical efficiency will be comparable.