PURPOSE: To make it possible to automatically display local time with the movement of a navigation body, by operating local time from a time differential signal and a standard time signal while adjusting the time displayed by a local time display timepiece to the local time.

CONSTITUTION: The present longitude and latitude of a ship are measured by an automatic ship's position measuring system 4 on the basis of the signal from an antenna 5 to the automatic ship position measuring system 4, and longitude and latitude informations are sent to CPU10 as a ship's position signal DS through an interface 6. CPU10 sends the longitude and latitude informations to memory 8 to read the time differential signal in the memory 8. Local standard time is operated from this time differential signal and the Greenwich mean time signal from a build-in timepiece 7 by CPU10 to calculate the difference between this local standard time and the presently displayed time and this difference signal is sent to a ship's clock 1 to obtain corrected local standard time and the presently displayed time and this difference signal is sent to a ship's clock 1 to obtain corrected local standard time.