  The Time Projection Chamber (TPC) can identify particle species using the
energy loss (dE/dx) measured by the readout pad rows. The dE/dx resolution for
the ILD (International Large Detector) -TPC for the International Linear
Collider experiment is expected to have high resolution for clear
identification. The dE/dx resolution of our prototype TPC with gating device
(gating GEM) to suppress ions feedback was measured using the electron test
beam in a magnet field at the facility in DESY. The dE/dx resolution for
ILD-TPC was estimated using this test beam data. The signal charge was measured
as a function of the incident angle of the beam. In this paper, we report on
the measurement of the signal charge and of the dE/dx resolution.
