We review our recent studies on ferromagnetic superconductors, UGe ₂, URhGe and UCoGe, where the spin-triplet state with the so-called equal spin pairing is realized.We focus on experimental results of URhGe and UCoGe in which the superconductivity occurs already at ambient pressure. The huge upper critical field H_c2 on UCoGe for the field along the hard magnetization axis (b-axis) is confirmed by the AC susceptibility measurements by the fine tuning of field angle. Contrary to the huge H_c2 along the hard-magnetization axis, H_c2 along the easy-magnetization axis (c-axis) is relatively small in value. However, the initial slope of H _c2, namely dH_c2/dT (H → 0) both in UCoGe and in URhGe indicates the large value, which can be explained by the magnetic domain effect detected in the magnetization measurements. The specific heat measurements using a high quality single crystal of UCoGe demonstrate the bulk superconductivity, which is extended under magnetic field for the field along c-axis.