Provided is an optical modulation element which includes an optical waveguide. The optical waveguide includes: a rib part; a first slab part extending from the first side face of the rib part; aid a second slab part extending from the second side face of the rib part. The optical waveguide includes a first semiconductor region and a second semiconductor region which have an opposite conductive type from each other. The first semiconductor region includes an upper section, a lateral section, and a lower section. The second semiconductor region is sandwiched between the upper section and the lower section so as to be substantially in direct contact with the upper section, the lateral section, and the lower section. At least one of an end face of the upper section and an end face of the lower section flushes with the first side face of the rib part.