A panel instrument to be mounted in a panel board, including: a main body having an outside dimension applicable to a first and a second panel instrument size standards; a display provided on one end of the main body and having an area that occupies a part of a front face of the panel board and is applicable to the first panel instrument size standard; a front panel mounted on a front face of the display; and a rear panel for holding the display with the front panel, wherein the rear panel has: first mounting holes that are provided on one diagonal line of the rear panel and correspond to a mounting hole standard applicable to the second panel instrument size standard; and second mounting holes that are provided on the other diagonal line and correspond to a mounting hole standard applicable to a third panel instrument size standard.