PROBLEM TO BE SOLVED: To improve visibility of display data of a biological information monitor without troubling an operator.SOLUTION: A biological information monitor having a biological information acquisition unit for acquiring biological information data of a patient and a display unit for displaying a measured value of the biological information data acquired in real time, includes: a detection unit for detecting change of a use environment of the biological information monitor and a display processing unit for changing a size or a font of a character of the measured value displayed depending on the change of the use environment of the biological information monitor detected by the detection unit.