Band-pass filter suppresses frequency components of a sound signal that are lower than a low-side cutoff frequency and that are higher than a high-side cutoff frequency. Pitch detection section detects a pitch of the sound signal having been processed by the band-pass filter. Target setting section variably sets a low-side target value lower than the pitch detected by the pitch detection section and a high-side target value higher than the detected pitch. Filter control section causes the low-side cutoff frequency to approach the low-side target value over time and causes the high-side cutoff frequency to approach the high-side target value over time. In this way, a pass band of the band-pass filter can be smoothly variably controlled in accordance with pitch change of the sound signal that is an object of pitch detection.