This paper presents the on-chip cellular mechanical impedance measurement by OCAIN (On-Chip Impedance ANalyzer). Robochip(robot integrated microfluidic chip) is installed in OCIAN as a disposable microfluidic component integrated with robotic sensing unit. For the high throughput sensing of cellular specimens, they are flown in the microchannel of Robochip and continuous multi-parameter sensing is carried out. For the cellular mechanical impedance measurement, a pair of width tunable wall and force sensor is integrated at the sensing area. One side of the wall is actuated in non-contact by the magnetic force, therefore, the wall is powerful enough to collapse a rigid cell and Robochip is disconnected with the outer magnetic driving system. These are quite advantageous, however, it was quite difficult to improve the position accuracy of the magnetically driven components in the chip. Here we succeeded in nanometric order tuning of the tunable wall width by the displacement reduction mechanism which was previously proposed by our group. Then we achieved cellular impedance measurement of flowing cells in the microchannel by nanometric tuning of the wall.