[en] The time variation of accretion rate of black spherules was measured at Norikura Cosmic-ray Observatory, Tokyo University. Remarkable periodic variation was not recognized in the results during the period of these experiments. From mineralogical and chemical investigation, it was found that large ilmenite spherule (400 μm diameter) and glassy magnetic spherule were contained in the collection of this work. Annual fall rate of the black spherule except ilmenite spherule on the earth are calculated to be 3.4 -- 4.0 x 10⁷ tons/year. (author)