A canned motor device includes a fixed seat, a motor unit, and a rear cover protector and a leakproof member. The rear cover protector has a main body portion disposed between a case body and a stator of the motor unit and sleeved around a cylindrical portion of the case body, and an extended portion connected to the main body portion, perpendicular to an axis, fluid-tightly abutting against a flange portion of the case body, and having an outer periphery that surrounds the axis and that has an outline larger than that of an annular periphery of the flange portion of the case body. The leakproof member is mounted between the flange portion of the case body and the extended portion of the rear cover protector.