This paper discusses the Josephson effect in superconductor/diffusive half metal/superconductor junctions. The spin-flip scattering at the junction interfaces opens a Josephson channel between the two spin-singlet superconductors. The odd-frequency equal-spin-triplet Cooper pairs carry the Josephson current. As a consequence, the local density of states in a half metal has a large peak at the Fermi energy. We propose an experimental method to detect odd-frequency pairs by using the scanning tunneling spectroscopy.