An image signal processing apparatus comprising: an input for receiving an image signal formed by: (a) double-speed conversion of a television signal and having a unit-frame formed of a plurality of fields comprising two fields of identical contents, or (b) double-speed conversion of a telecine converted signal and having a unit-frame formed of four fields comprising two fields of identical contents; sequence detection means for calculating for the received image signal difference value in pixel signal level between a detected pixel in a current field and a detected pixel at the same position in a field which comes one frame behind the current field, an d for specifying a first field in a unit-frame based on the difference value; motion vector detection means connected to the sequence detection means for detecting a motion vector for a field which comes k frames behind the current field, with respect to the detected pixel in the current field, wherein k=1 if the received image signal is formed by double-speed conversion of a television signal, and k=2 if the received image signal is formed by double-speed conversion of a telecine converted signal; data calculation means for calculating interpolation pixel data for the detected pixel based on the pixel data of the detected pixel in the current field and the pixel data of each pixel in the field which comes k frames behind the current field; and image control means for writing the interpolation pixel data into the pixel position obtained by shifting the position of the detected pixel in the current field in a direction along the motion vector, for a field in a unit-frame subsequent to the first field, the image control means for sequentially increasing the amount with which the position of the detected pixel is shifted every time the field shifts from the first field to the subsequent fields in the unit-frame within a range of a vector quantity of the detected motion vector. an input for receiving an image signal formed by: (a) double-speed conversion of a television signal and having a unit-frame formed of a plurality of fields comprising two fields of identical contents, or (b) double-speed conversion of a telecine converted signal and having a unit-frame formed of four fields comprising two fields of identical contents; sequence detection means for calculating for the received image signal difference value in pixel signal level between a detected pixel in a current field and a detected pixel at the same position in a field which comes one frame behind the current field, an d for specifying a first field in a unit-frame based on the difference value; motion vector detection means connected to the sequence detection means for detecting a motion vector for a field which comes k frames behind the current field, with respect to the detected pixel in the current field, wherein k=1 if the received image signal is formed by double-speed conversion of a television signal, and k=2 if the received image signal is formed by double-speed conversion of a telecine converted signal; data calculation means for calculating interpolation pixel data for the detected pixel based on the pixel data of the detected pixel in the current field and the pixel data of each pixel in the field which comes k frames behind the current field; and image control means for writing the interpolation pixel data into the pixel position obtained by shifting the position of the detected pixel in the current field in a direction along the motion vector, for a field in a unit-frame subsequent to the first field, the image control means for sequentially increasing the amount with which the position of the detected pixel is shifted every time the field shifts from the first field to the subsequent fields in the unit-frame within a range of a vector quantity of the detected motion vector.