An optical modulation device 1 includes a supporting body 2 including a pair of grooves 2b, 2c and a protrusion 2d between the grooves, a ridge par 6 including a channel type optical waveguide capable of multi mode propagation, a first side plate part 3A formed in a first side of the ridge part 6, a second side plate part 3B formed in a second side of the ridge part, a first adhesive layer 4A adhering the first side plate part 3A and the supporting body 2, a second adhesive layer 4B adhering the second side plate part 3B and the supporting body 2, and a third adhesive layer 4C adhering the ridge part 6 and the protrusion 2d. The device 1 further includes a first electrode 7A provided on a side face 6b of the ridge part on the first groove side, and a side face 3b and an upper face 3c of the first side plate part, and a second electrode 7B provided on a side face 6c of the ridge part 6 in the second groove side, the second groove 2c and a side face 3b and an upper face 3c of the second side plate part 3B. The first electrode 7A and the second electrode 7B apply a modulation voltage modulating light propagating in the channel type optical waveguide.