to the directions of the double headed arrows shown in the drawings as shown in fig1 and 2 the imaging unit 1 is provided with a first lens group unit 3 a body module 15 a board module 65 and a cover 76 that constitute the major components of the imaging unit 1 the first lens group unit 3 is provided with a holder 4 that is formed as a synthetic resin molded product the holder 4 is provided at the left end thereof with a pair of upper and lower lugs 5 each of which has a through hole 6 as shown in fig5 a prism accommodating space 7 which is open at the front and right sides is formed in the holder 4 the holder 4 is provided at the front opening of the prism accommodating space 7 with a front lens holding hole lens holding hole 8 which is open at a left portion thereof and is provided at the right opening of the prism accommodating space 7 with a right lens holding hole 9 which is noncircular in shape and open at the upper and lower ends thereof as shown in fig5 and other drawings the first lens group unit 3 is provided with a first prism.