A reference point detection light-receiving unit receives light from a reference point detection pattern by first to fifth light-receiving elements. The first to fifth light-receiving elements are arranged in a first direction and outputs first to fifth signals, respectively. A reference signal generation circuit outputs a reference signal that starts at a period where a level of a signal, which is obtained by adding first and second signals, and a level of a signal, which is obtained by adding third and fourth signals, will become equal, and ends at a period where a level of a signal, which is obtained by adding the second and third signals, and a level of a signal, which is obtained by adding fourth and fifth signals, become equal.