Optical unit, smartphone, and manufacturing method of optical unit

An optical unit comprising:

• an optical element that reflects light traveling on one side in a first direction to one side in a second direction intersecting the first direction;
• and
• a holder that holds the optical element, wherein
• the holder includes
• a holder body that extends in a third direction intersecting the first direction and the second direction, and
• a pair of side surface portions that extend from the holder body in an intersection direction intersecting the third direction,
• the optical element is arranged between the pair of side surface portions,
• at least one of the pair of side surfaces includes
• an inner side surface facing the optical element,
• an end surface connected to an edge of the inner side surface in the intersection direction and extending in the third direction, and
• a concave portion that is arranged astride the inner side surface and the end surface and is recessed in the intersection direction from the end surface,
• the concave portion accommodates an adhesive member that bonds the optical element with the holder, and
• a length of the concave portion in a direction along the end surface is greater than a depth of the concave portion in the intersection direction.