in tokyo/osaka....
some digicams are slightly cheaper (depending on exchange rates) but most are more expensive. for accessories, they have more choices, some are cheaper, some you cannot find locally in singapore, some are more expensive...so depending on what you want to buy.
normally i would buy stuffs like canon500D, nikon SD-8a, nikon eyepiece set, body cap, lens cap, camera straps...etc...all these small items...they're much much cheaper than singapore, and even cheaper than ordering from B&H, or any online stores..
generally, camera bodies, lenses, imported bag, imported tripods..or anything imported, are more expensive in tokyo.
not sure about rest of japan.