Ocean bottom pressure (OBP) data for tsunami monitoring obtained by cabled seafloor observatories deployed around Japan are known to be significantly affected by temperature changes. We investigated long-term changes of the OBP data including this OBP-temperature relationship using more than ten-year data. The yearly mean OBP changes were found to show gradual increase (O(hPa/year)), and to have no significant correlation to the temperature changes. In contrast, the strong relationship was apparent at periods from hours to days, and we tried to correct the OBP data based on the estimated OBP-temperature relationship. At periods longer than days, noise reduction was not enough for most of the corrected OBP data; however, it turned out that the correction works successfully for the data at a station off Hokkaido (KPG2) in detecting geophysical signals.