An upgrade of the long baseline neutrino experiment T2K near detector ND280 is currently being developed with the goal to reduce systematic uncertainties in the prediction of number of events at the far detector Super-Kamiokande. The upgrade program includes the design and construction of a new highly granular fully active scintillator detector with 3D WLS fiber readout as a neutrino target. The detector of about 200×180×60 cm3 in size and a mass of ∼2.2~tons will be assembled from about 2×106 plastic scintillator cubes of 1×1×1 cm3. Each cube is read out by three orthogonal Kuraray Y11 Wave Length Shifting (WLS) fibers threaded through the detector. Currently beam tests of two prototype of new detector were done. And the tests of individual elements of the detector are continuing.