A fish depth monitor is a device that can display first water depth data that indicates the location of terminal tackle that is engaged on fishing line reeled out from a spool, and second water depth data that indicates the location of the bottom of a fishing location transmitted from a fish finder, and includes a case, first and second reception portions, a display unit, and a control unit. The first and second reception portions receive the first water depth data from an electric driven reel and the second water depth data from the fish finder. The control unit graphically displays the received first and second water depth data in positions that correspond to the water depth on the display unit. It is possible to intuitively determine the positional relationship between the location of the terminal tackle and the location of the bottom.