An ultrasonic trimming apparatus is composed of an articulated robot, a cutting apparatus, and a grindstone. The cutting apparatus is composed of an ultrasonic oscillator which is supported by the end portion of the articulated robot, a cutter blade which is supported by the ultrasonic oscillator, and a workpiece securing portion which secures a workpiece. The grindstone serving as a grinding member is disposed within the movable range of the cutter blade driven by the robot and is placed in a position at which the cutter blade can pressure contact the cutter blade. The cutter blade is ultrasonically vibrated by the ultrasonic oscillator and is ground while being pressed against the grindstone by means of the articulated robot. The ultrasonic trimming apparatus efficiently cuts a sheet material composed of soft material such as plastic, fabric, or rubber, a composite material, or a material containing glass fiber by means of an environmentally conscious method even when the material has a three-dimensional shape.