To provide a multiplexing unit for a signal optical pulse which can give a time delay by spatially separating a signal optical pulse without variation in a propagation direction by wavelength contained in the signal optical pulse, and to provide a time resolved measuring device using it.

The signal optical pulse multiplexing unit includes a mirror 11, a half-mirror 12, N variable mirrors 131, 132, ..., 13N. The mirror 11 and the half-mirror 12 are mutually arranged in parallel, and each of the N variable mirrors is arranged so as to be parallel to the half-mirror 12 in the reverse side of the mirror 11 by sandwiching the half-mirror 12, and when an interval between the half-mirror 12 and the mirror 11 is D, it is arranged from one end of the half-mirror 12 to the other end so that the interval with the half-mirror satisfies D+Δ, D+2Δ, ... , D+NΔ. In addition, each of the N variable mirrors is vertically and movably composed in a normal direction so that Δ value is variable.