PURPOSE: To make it possible to adjust color purity with a high precision, by providing plural photoelectric conversion elements, vertical and horizontal deflecting coils, a peak holding circuit, a detection pulse processing circuit including a sample holding circuit, and a saw tooth wave generating circuit.

CONSTITUTION: Photoelectric conversion elements 1 and 39 are arranged in the left and the right in the front of the color CRT. Deflecting magnetic field generator 5 flows deflecting currents, which are synchronized with the vertical scanning period of the TV receiver and have the phase difference of 90°, to vertical deflection coils 41 and 42 and horizontal deflecting coils 43 and 44 provided in proper positions in the left and the right in the front of the CRT to generate deflecting magnetic fields in vertical and horizontal directions. Detection pulse processing circuits 48 and 49 are formed with the same circuits and function symmetrically for adjustment of the position of the deflecting coil, which is not shown in the figure, which is one of color purity adjustment works of the color TV, and these circuits 48 and 49 perform the same operations. Processing circuit 48 includes peak holding circuits 12∼15, sample holding circuits 20∼23, and differential amplifying circuits 29 and 30. Saw tooth wave generator 36 superposes the output on outputs of differential amplifiers 29 and 30 synchronously with oscillator 34 for display.