A method of evaluating a result of measurement of a blood volume by an apparatus for measuring the blood volume, the method comprising: • reading of at least sex, age and body surface area as specific information of a patient; • reading of a value of a coefficient α being the ratio of the variation of pulse pressure to that of the pulse wave propagation time of a subject, and of a value γ1 being a predetermined threshold (S72'); • displaying a request, if a value for β is not available, to measure a blood pressure, a pulse wave propagation time, and a heart rate, storing said values in registers PP1, PWTT1 and HR1, respectively, and calculating β from the expression β = PP1 - α · PWTT1; • displaying a request, if a value for K is not available, to input a CO value for calibration and store said value in a register C01, and calculating K from the expression K = C01 / {(α · PWTT1+ β) · HR1}; • calculating a second blood volume from the expression CO2 = a+b·Sex+c·Age+d·BSA+e·PWTT1+f·HR1·PP1, where CO2 is the second blood volume, Sex is the sex, when the subject is male, Sex = 1, and when the subject is female, Sex = -1; Age is the age; BSA is the body surface area; and a, b, c, d, e and f are constants; • calculating and displaying a first blood volume (esCO), based on a pulse wave propagation time (PWTT) and a heart rate of the subject, from the expression esCO = (αK · PWTT+ βK), where esCO is the first blood volume, αK and βK are coefficients inherent to the subject; • calculating a third blood volume by an expression of CO3 = a+b·Sex+c·Age+d·BSA+e·PWTT+f·HR·PP, where CO3 is the third blood volume, Sex is the sex, when the subject is male, Sex = 1, and when the subject is female, Sex = -1; Age is the age; BSA is the body surface area; and a, b, c, d, e and f are constants; • calculating an evaluation value γ representing the degree of coincidence between esCO and CO3 by an expression γ = (esCO - CO1)/CO1 - (CO3-CO2)/CO2; and • determining whether the absolute value of the calculated evaluation value γ is larger than the predetermined threshold γ1. • reading of at least sex, age and body surface area as specific information of a patient; • reading of a value of a coefficient α being the ratio of the variation of pulse pressure to that of the pulse wave propagation time of a subject, and of a value γ1 being a predetermined threshold (S72'); • displaying a request, if a value for β is not available, to measure a blood pressure, a pulse wave propagation time, and a heart rate, storing said values in registers PP1, PWTT1 and HR1, respectively, and calculating β from the expression β = PP1 - α · PWTT1; • displaying a request, if a value for K is not available, to input a CO value for calibration and store said value in a register C01, and calculating K from the expression K = C01 / {(α · PWTT1+ β) · HR1}; • calculating a second blood volume from the expression CO2 = a+b·Sex+c·Age+d·BSA+e·PWTT1+f·HR1·PP1, where CO2 is the second blood volume, Sex is the sex, when the subject is male, Sex = 1, and when the subject is female, Sex = -1; Age is the age; BSA is the body surface area; and a, b, c, d, e and f are constants; • calculating and displaying a first blood volume (esCO), based on a pulse wave propagation time (PWTT) and a heart rate of the subject, from the expression esCO = (αK · PWTT+ βK), where esCO is the first blood volume, αK and βK are coefficients inherent to the subject; • calculating a third blood volume by an expression of CO3 = a+b·Sex+c·Age+d·BSA+e·PWTT+f·HR·PP, where CO3 is the third blood volume, Sex is the sex, when the subject is male, Sex = 1, and when the subject is female, Sex = -1; Age is the age; BSA is the body surface area; and a, b, c, d, e and f are constants; • calculating an evaluation value γ representing the degree of coincidence between esCO and CO3 by an expression γ = (esCO - CO1)/CO1 - (CO3-CO2)/CO2; and • determining whether the absolute value of the calculated evaluation value γ is larger than the predetermined threshold γ1.