An synthesized electrocardiogram generating apparatus comprising: a lead waveform calculating unit which is configured to calculate a plurality of lead waveforms based on measured lead potentials of living body portions; a population coefficient calculating unit which is configured to calculate: first population coefficients (G) for a population of a predetermined number of persons which synthesize additional B leads from A leads containing a predetermined lead waveform in the plurality of lead waveforms, wherein A is an integer of four or more and B is an integer of one or more; and second population coefficients (G) for the population which synthesize additional D leads from C leads being smaller in number of lead waveforms than the A leads, by using the predetermined lead waveform of the A leads, wherein C is an integer of three or more and A - 1 or less and D is A - C; characterized by a personal coefficient calculating unit which is configured to calculate: first personal coefficients (Pe) for each person of the population which synthesize the B leads from the A leads; and second personal coefficients (Pe) for each person of the population which synthesize the D leads from the C leads; and a lead deriving unit which is configured to: calculate first specific personal coefficients (Pep) of a specific subject based on: a relationship between a magnitude of a ratio of the first population coefficients to the second population coefficients, and a magnitude of a ratio of the first personal coefficients (Pe) to the second personal coefficients (Pe); and second specific personal coefficients (Pep) of the specific subject which are calculated based on A leads of the specific subject, the A leads being acquired by electrocardiogram measurement; and synthesize B leads of the specific subject by using the first specific personal coefficients of the specific subject. a lead waveform calculating unit which is configured to calculate a plurality of lead waveforms based on measured lead potentials of living body portions; a population coefficient calculating unit which is configured to calculate: first population coefficients (G) for a population of a predetermined number of persons which synthesize additional B leads from A leads containing a predetermined lead waveform in the plurality of lead waveforms, wherein A is an integer of four or more and B is an integer of one or more; and second population coefficients (G) for the population which synthesize additional D leads from C leads being smaller in number of lead waveforms than the A leads, by using the predetermined lead waveform of the A leads, wherein C is an integer of three or more and A - 1 or less and D is A - C; first population coefficients (G) for a population of a predetermined number of persons which synthesize additional B leads from A leads containing a predetermined lead waveform in the plurality of lead waveforms, wherein A is an integer of four or more and B is an integer of one or more; and second population coefficients (G) for the population which synthesize additional D leads from C leads being smaller in number of lead waveforms than the A leads, by using the predetermined lead waveform of the A leads, wherein C is an integer of three or more and A - 1 or less and D is A - C; characterized by a personal coefficient calculating unit which is configured to calculate: first personal coefficients (Pe) for each person of the population which synthesize the B leads from the A leads; and second personal coefficients (Pe) for each person of the population which synthesize the D leads from the C leads; and first personal coefficients (Pe) for each person of the population which synthesize the B leads from the A leads; and second personal coefficients (Pe) for each person of the population which synthesize the D leads from the C leads; and a lead deriving unit which is configured to: calculate first specific personal coefficients (Pep) of a specific subject based on: a relationship between a magnitude of a ratio of the first population coefficients to the second population coefficients, and a magnitude of a ratio of the first personal coefficients (Pe) to the second personal coefficients (Pe); and second specific personal coefficients (Pep) of the specific subject which are calculated based on A leads of the specific subject, the A leads being acquired by electrocardiogram measurement; and synthesize B leads of the specific subject by using the first specific personal coefficients of the specific subject. calculate first specific personal coefficients (Pep) of a specific subject based on: a relationship between a magnitude of a ratio of the first population coefficients to the second population coefficients, and a magnitude of a ratio of the first personal coefficients (Pe) to the second personal coefficients (Pe); and second specific personal coefficients (Pep) of the specific subject which are calculated based on A leads of the specific subject, the A leads being acquired by electrocardiogram measurement; and a relationship between a magnitude of a ratio of the first population coefficients to the second population coefficients, and a magnitude of a ratio of the first personal coefficients (Pe) to the second personal coefficients (Pe); and second specific personal coefficients (Pep) of the specific subject which are calculated based on A leads of the specific subject, the A leads being acquired by electrocardiogram measurement; and synthesize B leads of the specific subject by using the first specific personal coefficients of the specific subject.