  The main goal of the T2K long-baseline neutrino experiment is the precise
measurement of the parameters of neutrino oscillation and the search for
CP-violation in the lepton sector. In 2017, the T2K collaboration launched the
Near Detector Upgrade project. This upgrade aims to reduce the systematic
errors of the oscillation parameters from 6-7% to 3-4%. In order to accomplish
such goal, ND280 Upgrade proposes to implement new upstream trackers to improve
the wide angle acceptance and low momentum threshold. One of the novel
technologies introduced in ND280 Upgrade is super fine-grained (SuperFGD)
scintillator target with 3D WLS fiber readout. The detector will consist of
about 2 million (192x184x56) scintillation cubes of 1-cm size. Each cube has
three orthogonal holes for WLS fibers to provide 3D optical readout. The total
mass of the detector is about 2 tons and the number of the readout channels is
about 60,000. This paper presents the current status of the development of this
detector.
