  We examine the possible phase diagram in an $H$-$T$ plane for
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in a two-band Pauli-limiting
superconductor. We here demonstrate that, as a result of the competition of two
different modulation length scales, the FFLO phase is divided into two phases
by the first-order transition: the $Q_1$- and $Q_2$-FFLO phases at the higher
and lower fields. The $Q_2$-FFLO phase is further divided by successive first
order transitions into an infinite family of FFLO subphases with rational
modulation vectors, forming a {\it devil's staircase structure} for the field
dependences of the modulation vector and paramagnetic moment. The critical
magnetic field above which the FFLO is stabilized is lower than that in a
single-band superconductor. However, the tricritical Lifshitz point $L$ at
$T_{\rm L}$ is invariant under two-band parameter changes.
