A light irradiating unit comprises an LED 5 and a housing 2 into which the LED 5 is incorporated and that has a heat dissipating portion wherein the housing 2 has a first housing element 21 and a second housing element 22 each of which is joined serially along a predetermined axial line, and further comprises a pressing arrangement 3 that fixes the LED 5 with pressure between a first pressing face 3b arranged at the first housing element 21 side and a second pressing face 3a arranged at the second housing element 22 side accompanied by joining the first and the second housing elements 21, 22 and a positioning arrangement 4 that positions the LED 5 so as to align an optical axis of the LED 5 with the predetermined axial line accompanied by joining the first and the second housing elements 21, 22.