The mass spectrum of the primordial black holes formed by density perturbation in the radiation-dominated era of the Randall-Sundrum type-2 cosmology is given .
The spectrum coincides with standard four-dimensional one on large scales but the deviation is apparent on smaller scales .
The mass spectrum is initially softer than standard four-dimensional one , while after accretion during the earliest era it becomes harder than that .
We also show expected extragalactic diffuse photon background spectra varying the initial perturbation power-law power spectrum and give constraints on the blue spectra and/or the reheating temperature .
The most recent observations on the small scale density perturbation from WMAP , SDSS and Lyman- \alpha Forest are used .
What we get are interpreted as constraints on the smaller-scale inflation on the brane connected to the larger one at the scale of Lyman- \alpha Forest .
If we set the bulk curvature radius to be 0.1 ~ { } \text { mm } and assume the reheating temperature is higher than 10 ^ { 6 } ~ { } \text { GeV } , the scalar spectral index from the smaller scale inflation is constrained to be n \lesssim 1.3 .
Typically , the constraints are tighter than the standard four-dimensional one , which is also revised by us using the most recent observations .