1. A processing apparatus for creating an avatar, comprising: a skeleton database to store statistics of skeleton sizes with respect to reference poses of a plurality of users; a function determination unit to determine a difference function representing a difference between a forward kinematics function, the forward kinematics function regarding joints of the avatar with respect to a reference pose of a target user, and positions of sensors attached to the target user, and to determine a skeleton prior function based on the statistics of the skeleton sizes with respect to the reference poses of the plurality of users; a calculation unit to calculate skeleton sizes of the joints of the avatar, and local coordinates corresponding to the sensors using at least one processor; and a display unit to display the avatar based on the calculated skeleton sizes of the joints and the calculated local coordinates.