To provide a method of detecting abnormal bone metabolism by using a gene strongly expressed in an osteoclast; a method of screening a compound having a therapeutic and/or preventive effect on abnormal bone metabolism; and a pharmaceutical composition for treating and/or preventing abnormal bone metabolism. Provision of a method of detecting abnormal bone metabolism by using the expression of human Siglec-15 gene as an index; a pharmaceutical composition containing an antibody which specifically recognizes human Siglec-15 and has an activity of inhibiting osteoclast formation; and the like.