A robot apparatus 1 is a four-legged mobile robot, and leg units 3A, 3B, 3C, and 3D are connected to the left and side parts in the front and rear sides of a body unit 2. Ahead unit 4 is connected to the front end of the body unit 2. The head unit 4 has a mouth (jaw) part capable of biting and holding a toy 200 shaped like a bone. The mouth part is constituted by upper and lower jaw parts, and adopts a structure capable of biting and securely holding a bite part 203 of the bone 200. A CPU as a control part executes programs according to an image recognition processing algorithm for recognizing the bone 200, a bone-bite control algorithm for biting the bone, and a bone-bite detection algorithm for detecting the bone.