A biological information monitor includes: a first measuring unit which measures a pulse wave propagation time of a patient; a second measuring unit which measures a blood pressure of the patient; a calculating unit which calculates an estimated blood pressure value of the patient based on the pulse wave propagation time of the patient; a setting unit which sets a threshold; and a determining unit which compares the estimated blood pressure value with the threshold. The second measuring unit is activated to measure the blood pressure of the patient at least one of at time intervals and at a time when an operator operates the second measuring unit, and the second measuring unit is activated to measure the blood pressure of the patient by the determining unit based on the comparison result.