A mark display unit for ship navigation, the mark display unit configured to display a plurality of marks on a display screen, each of the plurality of marks associated with a geographical position as indicated by latitude and longitude, comprising: a dial selector with a push function, a push operation of the dial selector being associated with selecting one of a plurality of categories corresponding to the number of push operations, and a rotational operation of the dial selector being associated with selecting one of a plurality of items regarding a selected category corresponding to the rotational position of the dial selector, the plurality of categories and the plurality of items assigned to the plurality of marks; and a controller configured to display on the display screen one or more of the marks in a reduced number obtained by narrowing-down of said plurality of marks, said narrowing-down defined by a combination of the number of push operations and the rotational position of the dial selector, wherein the mark display unit is configured to enable the user to register a mark indicating a fishing spot and additional information including at least one of a date and time of the fishing activity, a bottom sediment, a water temperature, a water depth, an age of the moon, a height of a tide, a direction of a current, and a flow speed of the current, the additional information being stored in association with each mark as additional information, wherein the selected item is switched among the plurality of items in association with the rotational operation of the dial selector, and as the selected item is switched, the controller displays one or more of the marks in the reduced number assigned with the item selected by the dial selector, by switching a display mode of each of the plurality of marks between a displayed mode and a not-displayed mode, each of the one or more of the marks displayed at a position on the display screen corresponding to the associated geographical position, wherein the controller displays, on the display screen, a window in which one of the categories and one of the items that are currently selected are displayed and the rest of the categories and the rest of the items that are currently not selected are not displayed. a dial selector with a push function, a push operation of the dial selector being associated with selecting one of a plurality of categories corresponding to the number of push operations, and a rotational operation of the dial selector being associated with selecting one of a plurality of items regarding a selected category corresponding to the rotational position of the dial selector, the plurality of categories and the plurality of items assigned to the plurality of marks; and a controller configured to display on the display screen one or more of the marks in a reduced number obtained by narrowing-down of said plurality of marks, said narrowing-down defined by a combination of the number of push operations and the rotational position of the dial selector, wherein the mark display unit is configured to enable the user to register a mark indicating a fishing spot and additional information including at least one of a date and time of the fishing activity, a bottom sediment, a water temperature, a water depth, an age of the moon, a height of a tide, a direction of a current, and a flow speed of the current, the additional information being stored in association with each mark as additional information, wherein the selected item is switched among the plurality of items in association with the rotational operation of the dial selector, and as the selected item is switched, the controller displays one or more of the marks in the reduced number assigned with the item selected by the dial selector, by switching a display mode of each of the plurality of marks between a displayed mode and a not-displayed mode, each of the one or more of the marks displayed at a position on the display screen corresponding to the associated geographical position, wherein the controller displays, on the display screen, a window in which one of the categories and one of the items that are currently selected are displayed and the rest of the categories and the rest of the items that are currently not selected are not displayed.