We experimentally demonstrated the amplification of optical disk readout signals by homodyne detection. This technique uses optical interference to amplify the signals. We further applied phase-diversity detection to reliably obtain the amplified readout signal. The optical system was carefully designed so that a sufficiently amplified readout signal can be obtained. In particular, we applied a corner cube prism as a reflection mirror to achieve sufficient stability of the interferometric optical system. We experimentally demonstrated a 3.6 times amplification of a Blu-ray Disc readout signal. The estimated signal-to-noise ratio (SNR) improvement for an assumed eight-layer optical disk readout signals by applying homodyne detection on the basis of the observed amplification was +7.9 dB, which significantly enables reliable readout of recorded signals. The present technique will be essential for the real commercialization of next-generation multilayer optical disk because of its outstanding ability of SNR improvement.