A similarity assessment apparatus is provided for assessing a performance sound based on a model performance sound. In the apparatus, a probability density function generating unit divides data of a performance sound into a sequence of frames each having a predetermined temporal length, and generates a probability density function of a fundamental frequency for each frame of the performance sound. A probability density function providing portion provides a probability density function of a fundamental frequency for each frame of the model performance sound. A similarity assessment unit compares the generated probability density function of a frame of the performance sound with the provided probability density function of a frame of the model performance sound so as to assess a similarity between the performance sound and the model performance sound.