1. A broadband light source unit, comprising: (a) a light source that outputs a first source lightwave, which is a pulse lightwave having pulses that are periodic and that have a constant intensity; (b) a conversion means that receives the first source lightwave, produces a second source lightwave having pulses whose intensities are different from one another, and outputs the second source lightwave; and (c) a nonlinear optical medium section that receives the second source lightwave, produces a supercontinuum lightwave having a wavelength band broadened by dint of a nonlinear optical phenomenon, and outputs the supercontinuum lightwave.