PURPOSE: To enable correct altitude correction by changing an atmospheric pressure value, converted by a converting means, to an atmospheric pressure value at 0 meter of sea level by an operating means.

CONSTITUTION: A pressure sensor 20 converts an atmospheric pressure value into an electric signal which is inputted to an amplifying circuit 19. An amplified signal 10a is fed to an A/D conversion circuit 18 which produces a digital signal 10b. The signal 10b is fed to an operating circuit 11 where it is operated as an atmospheric pressure value and stored in a RAM 12. An atmospheric pressure value corrected at sea level can be displayed by operating an external operating switch. When the atmospheric pressure value at an altitude of 40m is 1008hPa, for example, following calculation is conducted and an atmospheric pressure value of 1013hPa is displayed. PSL=1013, 25-Po(Alt)+P, where PSL is the atmospheric pressure value corrected at the sea level, Po(Alt) is an atmospheric pressure value determined from ICAO standard atmospheric, and P is a measured atmospheric pressure. Thus corrected atmospheric pressure value can be used effectively as one data for deciding the weather.