PURPOSE: To match a variable mark with a target video, by varying the speed of pulses for variable mark setting, and making the movement speed of the variable mark nearly constant regardless of a detection range.

CONSTITUTION: The needle of the setting operation switch 27 of a setting operation means 21 for the variable mark is grounded, and connected selectively to three positions, i.e. neutral point N which is not connected to any point, increase terminal U, and decrease terminal D. An increase or decrease pulse from the terminal 23 or 24 is counted by a up/down counter 25. The count contents of the counter 25 are preset in a down counter 26. When the contents of the down counter 26 go down to zero on the basis of a clock from a clock generator 27, a varaible mark signal is outputted from a terminal 28.