Abstract: A light source unit (60) used for a vehicular head-up display according to the present invention is provided with: a tubular multi-reflection member (61) which connects an entrance plane (63) and an exit plane (64) and which has a reflecting plane (66) provided on an inner surface thereof; and a substrate (62) which is disposed so as to face the entrance plane (63) and on which a plurality of light sources (65) are mounted in a matrix configuration. The ratio Ra=AB between the number A of light sources (65) disposed in a long-axis direction (X) of the entrance plane (63) and the number (B) of light sources (65) disposed in a short-axis direction (Y) of the entrance plane (63) is configured to be greater than the ratio Rb=C/D between the long-axis dimension C and the short-axis dimension D of the exit plane (64).