A novel flexible neural interface device was proposed, designed and fabricated. The device realizes electrical stimulation and measurement of neural tissues using an array of smart electrodes. The smart electrode has intelligence by dedicated CMOS microchip. Thanks to the smart electrodes high functions of the array with large number of electrodes are obtained only with 4 wiring connected to external equipments. Moreover, the device has enough flexibility for low invasion to the living body tissues. As one of in vivo evaluations, retinal stimulation was performed with the device using an experimental animal. Stimulus function of the device implanted into the living body was demonstrated successfully, responses caused by the stimulation were observed.