A first angle acquiring unit acquires a rotational angle of a characteristic portion in a predetermined region on an inlet side of an insertion member of a linear body extending through the insertion member. From an image of the linear body inserted into a body of a subject, a second angle acquiring unit acquires a direction of a curved portion of the linear body inserted into the body of the subject and then acquires a rotational angle of a distal end of the linear body. A torque calculation unit calculates a torque based on a difference between the rotational angle in the predetermined region acquired by the first angle acquiring unit and the rotational angle of the distal end of the linear body acquired by the second angle acquiring unit.