To provide a cardiac sound measuring device, an optimum exercise intensity measuring device, a cardiac sound measuring method and a cardiac sound measuring program, capable of automatically measuring the optimum exercise intensity by accurately and easily measuring a first cardiac sound during loading exercise.

The optimum exercise intensity measuring device 1 comprises: a cardiac sound collecting means 2 including a cardiac sound microphone 21 for collecting cardiac sound and an A-D converting means 23 for converting cardiac sound signals to cardiac sound data; an electrocardiac collecting means 3 including a measuring electrode 31 for collecting electrocardiac signals and an A-D converting means 33 for converting the electrocardiac signals from the measuring electrode 31 to electrocardiac data; a reference timing detecting means 43 for detecting R-waves from the electrocardiac data; a gate signal generating means 44 for outputting gate signals indicating a prescribed period from the timing of the R-waves detected by the reference timing detecting means 43 before second cardiac sound corresponding to the R-waves; and a first cardiac sound detecting means 45 for extracting the peak waveform as first cardiac sound amplitude data from the cardiac sound data while the gate signals are output.