device 13 makes a display indicating that the first table is in use at a step s3 the switch 12 which is provided for change over of the tables is checked to see if it has been pushed if not the flow of operation comes to a step s5 if it is found to have been pushed the flow comes to a step s4 to change the use of the table from the table currently in use over to a next table and then comes to the step s5 in case that the table being currently in use happens to be the last table at the step s4 the use of the table comes back to the first table then the display device 13 makes a display showing which of the tables is currently in use at the step s5 the gain control signals v rc and v bc which have been initially set as mentioned above are supplied via the d a converters 11a and 11b to the r amplifier 2 and the b amplifier 3 respectively at a step s6 the reference voltage v s is read via the a d converter 9c at a step s7 the integration outputs r y 39 and b y 39 of the integration circuits 7 and 8 are.