An abnormality diagnosis device of an in-cylinder pressure sensor is provided. The device carries out a performance determination in which a performance quality of the sensor is determined based on an electric signal inputted from the sensor. The device carries out a first determination in which the performance determination is performed at a given timing, a performance recovery in which a given deposit removal control is executed in which a deposit accumulating inside the combustion chamber is removed when the performance quality of the in-cylinder pressure sensor is determined to fall below a given reference value, and a second determination in which the performance determination is carried out again after the performance recovery. In the second determination, the in-cylinder pressure sensor is diagnosed as abnormal when the performance quality of the sensor is determined to fall below the given reference value.