NOVELTY - The photo-interrupter has an insulating base (2) including insulating substrates, and light emitting and receiving elements (10, 15) are provided at an upper surface of the substrate. Two terminal electrodes are provided for light emitting and receiving elements, respectively. Two primary molds (30, 31) cover the elements and are provided with inclined surfaces (37, 38). A secondary mold (32) is provided with a groove (34) located between the primary molds and includes a light shielding portion (35), where light generated by the emitting element traverses to reach the receiving element.    USE - Used for detecting an object passing via a groove.    ADVANTAGE - The configuration of the photo-interrupter eliminates the need for a lead made of metal plate, thus allowing the photo-interrupter to be compact in size and weight and requiring a small space for soldering, and hence reducing the manufacturing cost of the photo-interrupter by using a single die. The light generated by the light emitting element traverses to reach the light receiving element, thus allowing reflecting surfaces at the primary molds to accurately guide the generated light to the light receiving element. The secondary mold includes the light shielding portion located between the primary molds, thus preventing the light generated by the light emitting element from reaching the light receiving element directly without passing through the groove, and hence improving the accuracy of detection of an object. The insulating base includes the insulating substrates, such that the deformation of the base due to external force or difference of thermal expansion is more effectively prevented, thus improving the accuracy of the detection of the object.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method of manufacturing a surface mount photo-interrupter.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the surface mount type photo-interrupter.    Insulating base (2)    Sub insulating substrate (4)    Through-holes (5a, 5b)    Light emitting element (10)    Light receiving element (15)    Primary molds (30, 31)    Secondary mold (32)    Groove (34)    Light shielding portion (35)    Transmission holes (36a, 36b)    Inclined surfaces (37, 38)