  The lightest Kaluza-Klein particle (LKP), which appears in the theory of
universal extra dimensions, is one of the good candidates for cold dark matter.
The gamma-ray spectrum from annihilation of LKP dark matter shows a
characteristic peak structure around the LKP mass. We investigate the
detectability of this peak structure by considering energy resolution of
near-future detectors, and calculate the expected count spectrum of the
gamma-ray signal. In order to judge whether the count spectrum contains the LKP
signal, the {\chi} squared test is employed. If the signal is not detected, we
set some constraints on the boost factor that is an uncertain factor dependent
on the substructure of the LKP distribution in the galactic halo. Detecting
such peak structure would be conclusive evidence that dark matter is made of
LKP.
