It is shown that the periodic stacked structures of nanocrystalline porous silicon (nc-PS) layers with controlled densities and elastic properties act as an acoustic band crystal (ABC) device. Supposing that the periodic nc-PS layers are formed by conventional modulated anodization technique to fabricate the multi-layered distributed Brag reflection mirror, the acoustic wave propagation modes are investigated theoretically for various structural parameters. According to the calculation results, a significant acoustic band gaps are generated in the ultrasonic regions due to a big contrast in the elastic constant produced between low-porosity and compact nc-PS layers. The propagation of acoustic wave can be completely suppressed in the characteristic band determined from designed parameters. The present result suggests further possibility of the nc-PS layer as a key component of ABC devices.