A foreign substance detection device for detecting a foreign substance adhered inside a pipe, comprising: - an electromechanical conversion element, which is attached to an outside of the pipe, and is configured to convert electric energy to mechanical energy and convert mechanical energy to electric energy; and - a foreign substance detection unit configured to measure impedance of the electromechanical conversion element to detect adhesion of a foreign substance inside the pipe, the foreign substance detection unit including: - a power source configured to supply power to the electromechanical conversion element to cause the electromechanical conversion element to vibrate; - a voltage measurement unit configured to measure an element voltage applied to the electromechanical conversion element when power is supplied from the power source; - a current measurement unit configured to measure an element current flowing through the electromechanical conversion element when power is supplied from the power source; - an impedance calculation unit configured to calculate the impedance based on the element voltage and the element current; and - a detection unit configured to detect adhesion of a foreign substance inside the pipe based on the impedance calculated by the impedance calculation unit, wherein the foreign substance detection unit further comprises a phase measurement unit configured to measure a phase difference between the element voltage measured by the voltage measurement unit and the element current measured by the current measurement unit, and wherein the impedance calculation unit is configured to calculate the impedance based on the element voltage, the element current, and the phase difference measured by the phase measurement unit, wherein a piezoelectric element is used as the electromechanical conversion element, wherein the power source is configured to drive the electromechanical conversion element to vibrate at a vibration frequency that is a resonance frequency, wherein the impedance calculation unit is configured to measure a resonance frequency of the electromechanical conversion element based on a result of the measurement of the impedance of the electromechanical conversion element, wherein the impedance calculation unit is configured to calculate the impedance every time the frequency of the power source is changed, based on the element voltage, the element current, and the phase difference measured by the phase measurement unit. - an electromechanical conversion element, which is attached to an outside of the pipe, and is configured to convert electric energy to mechanical energy and convert mechanical energy to electric energy; and - a foreign substance detection unit configured to measure impedance of the electromechanical conversion element to detect adhesion of a foreign substance inside the pipe, the foreign substance detection unit including: - a power source configured to supply power to the electromechanical conversion element to cause the electromechanical conversion element to vibrate; - a voltage measurement unit configured to measure an element voltage applied to the electromechanical conversion element when power is supplied from the power source; - a current measurement unit configured to measure an element current flowing through the electromechanical conversion element when power is supplied from the power source; - an impedance calculation unit configured to calculate the impedance based on the element voltage and the element current; and - a detection unit configured to detect adhesion of a foreign substance inside the pipe based on the impedance calculated by the impedance calculation unit, - a power source configured to supply power to the electromechanical conversion element to cause the electromechanical conversion element to vibrate; - a voltage measurement unit configured to measure an element voltage applied to the electromechanical conversion element when power is supplied from the power source; - a current measurement unit configured to measure an element current flowing through the electromechanical conversion element when power is supplied from the power source; - an impedance calculation unit configured to calculate the impedance based on the element voltage and the element current; and - a detection unit configured to detect adhesion of a foreign substance inside the pipe based on the impedance calculated by the impedance calculation unit, wherein the foreign substance detection unit further comprises a phase measurement unit configured to measure a phase difference between the element voltage measured by the voltage measurement unit and the element current measured by the current measurement unit, and wherein the impedance calculation unit is configured to calculate the impedance based on the element voltage, the element current, and the phase difference measured by the phase measurement unit, wherein a piezoelectric element is used as the electromechanical conversion element, wherein the power source is configured to drive the electromechanical conversion element to vibrate at a vibration frequency that is a resonance frequency, wherein the impedance calculation unit is configured to measure a resonance frequency of the electromechanical conversion element based on a result of the measurement of the impedance of the electromechanical conversion element, wherein the impedance calculation unit is configured to calculate the impedance every time the frequency of the power source is changed, based on the element voltage, the element current, and the phase difference measured by the phase measurement unit.