Signal processing device, sonic system and vehicle

A signal processing device, comprising:

• a transmission signal generation unit, configured to generate a transmission signal for a transmitted wave of sound wave;
• a reception signal output unit, configured to output a received signal based on a received wave of sound wave;
• and
• a reflected wave detection unit, wherein the reflected wave detection unit is configured to detect a first reflected wave of the transmitted wave that is included in the received wave based on a positive time rate of change of an envelope detection signal, which is a signal obtained by envelope detection of an absolute value of the received signal in a reverberation period in which a reverberation of the transmitted wave remains, wherein the reflected wave detection unit is configured to detect the first reflected wave based on an integral value of the positive time rate of change, and wherein the integral value exceeds a threshold value.