  We present the first measurement of the metallicity gradient in extremely
metal-poor galaxies (EMPGs). With Subaru/Faint Object Camera And Spectrograph
(FOCAS) Integral Field Unit (IFU), we have observed a nearby, low-mass EMPG,
HSC J1631+4426, whose oxygen abundance and stellar mass are known to be
12+log(O/H) $=6.9$ and $\log_{10}(M_*/{\rm M}_\odot)=5.8$, respectively. The
measured metallicity gradient is $-0.36 \pm 0.04$ dex kpc$^{-1}$ corresponding
to $-0.049 \pm 0.006$ dex R$_\mathrm{e}^{-1}$ for the continuum effective
radius of $R_\mathrm{e} = 0.14$ kpc. Our observation has successfully
demonstrated that three-dimensional spectroscopy with 8m-class telescopes is
powerful enough to reveal the metallicity distribution in local EMPGs,
providing precious information of the baryon cycle in local analogs of
primordial galaxies in the early Universe.
