PURPOSE:To obtain still pictures by using properly three analog memories by turns for reading and writing operation. CONSTITUTION:For example, it is assumed that the current input signal is represented by signal C and the last input signal by signal B. In this case, when the switch is operated to project a still picture on the subordinate screen, signal B has been stored in analog memory 6, and signal C is being written in analog memory 8. At this time, while output signal B is read out of analog memory 6, this signal B is written in analog memory 7. Next, while output signal C is read out of analog memory 8, this signal C is written in analog memory 6. Further, signal B is read out of analog memory 7 and thus the signals are circulated to obtain the still picture.