A method and apparatus are provided for separating thigh meat and oyster meat from the thighbone automatically without detecting the boundary of the white cap at an end of the thigh bone and the meat including thigh meat and oyster meat and inserting a cutter into the detected boundary part in the final operation of deboning a thigh-with-bone of an edible beast and bird. The apparatus of the invention for separating thigh meat and oyster meat is composed of a clamper 15, a Y-shaped guide-with-a-groove 20, and a Y-shaped guide-with-a-cutter 16 downstream of the guide 20 provided on the transfer line of the clamper, both guides being provided such that the open end side of Y-shape of each guide is directed toward upstream of transfer of the clamper.