Calcification (biomineralization) is essential for maintenance of a life. The elucidation of "Osteoclast-mediated demineralization of biomineral" directly links elucidation for bone mineral balance (coupling of bone tissue). Bone is continuously destroyed and reformed in vertebrates to maintain bone volume and calcium homeostasis. In this review, we summarize the regulatory mechanism of osteoclast-mediated demineralization of biomineral by osteoblast-derived osteoclast differentiation factor (RANKL).