reference value is as follows a u03b4w u03b4t 2 j inertia a rotational acceleration of the drum t input torque u03b4w variation of angular velocity of the drum difference between the first reference value and the second reference value u03b4t time variation according to the above equations multiplication of the inertia j and the rotational acceleration a of the drum 12 corresponds to the input torque t the input torque t is a physical factor causing the drum 12 to rotate and the input torque t is set as a constant by the control unit 31 the rotational acceleration is variation of the rotational speed of the drum 12 with respect to time and is measured by the rpm detection unit 33 accordingly the inertia is detected through the equation described below that is if the control unit 31 receives information u03b4w u03b4t on the angular velocity of the drum 12 with respect to a predetermined time from the rpm detection unit 33 the control unit 33 multiplies the information on the angular velocity by the torque t having a constant thereby obtaining the inertia j meanwhile the weight estimated by the drum 12 or the drum 12 and the clothes can be obtained through the equation described below using the reference value as described the above equation the weight estimated by the drum 12 or the drum 12 and the clothes can be obtained by multiplying the estimated inertia j by the constant k the above equation 4 represents that the estimated inertia is proportional to the estimated weight and the constant k is determined by a designer through various experiments in.