A user is asked to perform tapping at beat positions by using a tapping detection section while listening to the beginning of a waveform from which beats are to be detected. When a fluctuation calculation section determines that tapping fluctuation falls in a predetermined range, a beat interval close in number to the tempo of the tapping is selected from among beat-interval candidates detected by a tempo-candidate detection section, and a tapping position where tapping becomes stable is determined to be the starting beat position. Tapping by the user for just some beats allows beats to be detected in the entire musical piece more correctly.