  We study the relation between luminosity and spin-period change in X-ray
binary pulsars using long-term light curve obtained by the MAXI/GSC all-sky
survey and pulse period data from the Fermi/GBM pulsar project. X-ray binaries,
consisting of a highly magnetized neutron star and a stellar companion,
originate X-ray emission according to the energy of the accretion matter onto
the neutron star. The accretion matter also transfers the angular momentum at
the Alfven radius, and then spin up the neutron star. Therefore, the X-ray
luminosity and the spin-up rate are supposed to be well correlated. We analyzed
the luminosity and period-change relation using the data taken by continuous
monitoring of MAXI/GSC and Fermi/GBM for Be/X-ray binaries, GX 304$-$1, A
0535$+$26, GRO J1008$-$57, KS 1947$+$300, and 2S 1417$-$624, which occurred
large outbursts in the last four years. We discuss the results comparing the
obtained observed relation with that of the theoretical model by Ghosh \& Lamb
(1979).
