A target assembly is provided in which an abnormal discharging between a projected portion of a backing plate and a side surface of the target is prevented and also in which a bonding material to bond the target and the backing plate can be surely prevented from seeping to the outside and also which is easy in reusing the backing plate. The target assembly according to this invention having: a target made of an insulating material; and a backing plate bonded to one surface of the target via a bonding material, the backing plate having a projected portion which is projected outward beyond an outer peripheral edge of the target, further has an annular insulating plate. The annular insulating plate: encloses a circumference of the target while maintaining a predetermined clearance to a side surface of the target; and covers that surface of the projected portion.