Edge states of topological systems have attracted great interest due to their robustness and linear dispersions. Here a superconducting-proximitized edge interferometer is engineered on a second-order topological insulator Ta2Pd3Te5 with symmetric edges to realize the interfering Josephson diode effect (JDE), which hosts many advantages, such as the high efficiency as much as 73% at tiny applied magnetic field with an ultra-low switching power around picowatt, and a giant interfering magnetochiral anisotropy with a maximal coefficient γ = 1.2 × 109 T− 1A−1 - three orders of magnitude larger than the reported record. As an important element to induce such JDE, the second-order harmonic in the current-phase relation is also experimentally confirmed by half Shapiro steps. This edge interferometer offers a novel and effective method to enhance the overall performance of JDE and magnetochiral anisotropy, and boosts great potential applications for future superconducting quantum devices.