Provided is a fuel-reforming device comprising: an
ammonia tank (4); a reformer (5) for reforming
ammonia and generating high-concentration
hydrogen gas having a
hydrogen content of at least 99%; a
mixing tank (7) for mixing
ammonia and
hydrogen for
temporary storage; and a control means (10) for controlling the respective supply amounts of ammonia and high-concentration hydrogen gas that are supplied to the
mixing tank (7). The control means (10) calculates the
combustion rate coefficient C of
mixed gas with respect to a reference fuel on the basis of equation (1). Equation (1): S0=SH*C+SA*(1-C). In equation (1), S0 is the
combustion rate of the reference fuel, SH is the
combustion rate of hydrogen, SA is the combustion rate of ammonia, and C is the combustion rate coefficient of
mixed gas. In addition, on the basis of equation (2), the control means (10) determines the volume fractions of ammonia and hydrogen that are supplied to the
mixing tank. Equation (2): C=1-exp(-A*MB). In equation (2), M is the
volume fraction of hydrogen in
mixed gas, and A and B are constants.