An image signal processing apparatus according to the present invention receives an image signal inputted thereto that is generated by subjecting a telecine-converted image to double speed conversion, in which signal one film frame is formed by four fields, identifies a first field on the basis of a difference value calculated between pixel signal levels, and shifts the position of a detected pixel in a vector direction of a motion vector such that an amount of shift is progressively increased as transition is made from the identified first field to the subsequent fields.