We focus on a compact continuous flow system to generate nanoemulsion in microchannels with ultrasonic vibration. This device is fabricated by the easily-stackable microchannel plates and an ultrasonic vibrating plate. Optimized oscillation frequency is 2.25 MHz. The cross-sectional pattern of the microchannels affects on not only the residence time but the efficiency of nanoemulsification. By optimizing the microchannels, we have succeeded in the production of nanoemulsion with 80 nm in a diameter.