A method for producing a photocoupler includes the steps of: forming a waveguide structure on a substrate; forming a photoresist layer having a groove on the waveguide structure; mounting a prism on the photoresist layer so as to partially cover the groove; bonding the prism on the waveguide structure by injecting an adhesive into the groove; and removing the photoresist layer. The groove has a T-shaped pattern including a transverse section extending in a first direction and a longitudinal section extending in a second direction perpendicular to the first direction. The transverse section has a first width in the second direction which is smaller than a second length of a bonding face of the prism in the second direction. The prism is bonded to the waveguide structure through the bonding face. The longitudinal section has a second width in the first direction which is smaller than a first length of the bonding face of the prism in the first direction. The transverse section has a first length in the first direction which is greater than the first length of the bonding face of the prism in the first direction. The longitudinal section has a second length in the second direction which is greater than the second length of the bonding face of the prism in the second direction. The adhesive is injected into an end portion of the longitudinal section which is distanced away from the transverse section, the end portion not being covered by the prism.