An autocorrelation measurement device includes a first reflection member, a second reflection member, a focusing unit, a nonlinear optical crystal, a detection unit, a filter, an aperture, a delay adjusting unit, and an analysis unit. Incident pulsed light is transmitted through the second reflection member and incident on the first reflection member. First pulsed light reflected on a first reflection surface of the first reflection member and a second reflection surface of the second reflection member and second pulsed light reflected on a second reflection surface of the first reflection member and a first reflection surface of the second reflection member are incident on the nonlinear optical crystal via the focusing unit. Second harmonic light generated in the nonlinear optical crystal is detected by the detection unit.