The localized spin wave modes are studied theoretically for insulating ferromagnet with an antiferromagnetic impurity, on the basis of the Heisenberg model with particular reference to the simple cubic lattice. Besides localized p and d modes, which are of the same type as seen in ferromagnet with a ferromagnetic impurity, we have one or two localized s modes for the present case depending on certain conditions. One of them is an antiferromagnetic mode, which comes out of the bottom of the spin wave band. This has no analogue in ferromagnet with a ferromagnetic impurity. The condition for the appearance of localized s modes, the zero-point contraction of spins, and the frequency shirt of localized modes due to magnetic field and anisotropy energy are studied.