A signal detection method including the steps of: initiating integration of charge signals by an integrating amplifier; holding a first electrical signal integrated by the integrating amplifier during a time period from the start of the integration to the end of a predetermined baseline sampling time, and passed through a first low-pass filter having a time constant τ1; and performing signal detection by obtaining the difference between a second electrical signal and the first electrical signal, the second electrical signal being an electrical signal integrated by the integrating amplifier during a time period from the start of the integration to a predetermined time point which is a time point before the integrating amplifier is reset after the first electrical signal is obtained, and passed through a second low-pass filter having a time constant τ2 which is greater than the time constant τ1.