A sander according to the present invention comprising a housing, a motor and a transmission mounted within the housing, a sanding plate mounted below the housing, a battery pack mounted at the rear end of the housing and a balancer mounted on either the housing or the sanding plate. The balancer includes a balance element disposed in the front part of the sander. The balance element is balanced with the battery pack, which solves the balance problem of the DC sanders known in the prior art while still providing a battery pack that can satisfy the power requirements of the sander.