Abstract: A photosensitizer containing guanidine derivative expressed in General Formula (a) as and a photosensitizer expressed in General Formula (X) as D(m+m?)?(A+)m(A?+)m? or in General Formula (Y) as D(m+m?+n)?(A+)m(A?+)m?(B+)n (where D has a molecular structure capable of absorbing visible light or infrared ray, A and A? represent the guanidine derivative, and B represents an ion other than the guanidine derivative), and a semiconductor electrode and a photoelectric conversion device employing the photosensitizer are provided. A photosensitizer having a novel structure as well as a semiconductor electrode and a photoelectric conversion device employing the photosensitizer are thus provided.