A biological signal measurement system comprising: a) biological electrodes (20, 21,22) capable of coming into contact with a surface of a living body; b) a biological signal measurement apparatus; c) a portable terminal; said biological signal measurement apparatus comprising (i) means for generating first biological digital data by quantizing, based on a first sampling rate, a biological electrical signal detected by the biological electrodes, (ii) means for extracting first feature amount data from the first biological digital data, (iii) means for generating second biological digital data downsized from the first biological digital data to a data size corresponding to a second sampling rate lower than the first sampling rate, (iv) wireless communication means for transmitting the second biological digital data and the first feature amount data to said portable terminal; said portable terminal comprising (i) means for receiving the second biological digital data and the first feature amount data, (ii) means for generating second feature amount data by performing statistical analysis of the first feature amount data, and (iii) means for displaying at least one of the second biological digital data and the second feature amount data, wherein the means for extracting first feature amount data and the means for generating second biological digital data are configured to use, as input data, the first biological digital data generated by the means for generating first biological digital data, and respectively output the first feature amount data and the second biological digital data, the biological electrical signal is an electrocardiogram signal, the first feature amount data is data including at least an R-R interval of the electrocardiogram signal, and the second feature amount data is data including one of a ratio of a low frequency spectrum component amount of a temporal fluctuation of the R-R interval to a high frequency spectrum component amount, a value obtained by dividing a standard deviation of R-R intervals by an average value of the R-R intervals, and a ratio of the number of R-R intervals for which a difference between two consecutive R-R intervals is not less than 50 msec to a predetermined number of R-R intervals. a) biological electrodes (20, 21,22) capable of coming into contact with a surface of a living body; b) a biological signal measurement apparatus; c) a portable terminal; said biological signal measurement apparatus comprising (i) means for generating first biological digital data by quantizing, based on a first sampling rate, a biological electrical signal detected by the biological electrodes, (ii) means for extracting first feature amount data from the first biological digital data, (iii) means for generating second biological digital data downsized from the first biological digital data to a data size corresponding to a second sampling rate lower than the first sampling rate, (iv) wireless communication means for transmitting the second biological digital data and the first feature amount data to said portable terminal; said portable terminal comprising (i) means for receiving the second biological digital data and the first feature amount data, (ii) means for generating second feature amount data by performing statistical analysis of the first feature amount data, and (iii) means for displaying at least one of the second biological digital data and the second feature amount data, wherein the means for extracting first feature amount data and the means for generating second biological digital data are configured to use, as input data, the first biological digital data generated by the means for generating first biological digital data, and respectively output the first feature amount data and the second biological digital data, the biological electrical signal is an electrocardiogram signal, the first feature amount data is data including at least an R-R interval of the electrocardiogram signal, and the second feature amount data is data including one of a ratio of a low frequency spectrum component amount of a temporal fluctuation of the R-R interval to a high frequency spectrum component amount, a value obtained by dividing a standard deviation of R-R intervals by an average value of the R-R intervals, and a ratio of the number of R-R intervals for which a difference between two consecutive R-R intervals is not less than 50 msec to a predetermined number of R-R intervals.