A cardiac muscle excitation waveform detector including: a waveform acquisition section that acquires, in a preset period, a waveform from an intracardiac electrocardiogram measured in middle of occurrence of atrial fibrillation; a waveform detection condition setting section that sets conditions for detecting a waveform of cardiac muscle excitation; and an excitation waveform detection section that detects a waveform of cardiac muscle excitation from the waveforms based on the conditions, wherein the waveform detection condition setting section includes a section that sets conditions based on a contour of a waveform to detect candidates for the waveform of cardiac muscle excitation, a section that sets a search period for searching for a waveform of cardiac muscle excitation; and a section that sets a preset period subsequent to detection as a detection exclusion period during which the candidate waveforms are not detected when the waveform of cardiac muscle excitation is detected.