To perform uniform liquid level measurement enabling non-dispersed operation by operators.

This liquid level measuring auxiliary tool used for a level gage of a container for storing liquid is equipped with a scale 11 arranged along the level gage, on which a scale from a reference position is put; and a cursor 12 held movably on the scale 11. The cursor 12 is operated to show a liquid level at a measuring time. An index part moved to a liquid level position at the measuring time can be held in the state where the liquid level at the measuring time is shown by this constitution.