In quartz diorite of the Koyama calc-alkaline intrusive, Susa, southwest Japan, small columnar crystals and needles of apatite are included in interstitial amphibole, biotite and quartz which have formed under late-magmatic oxidizing condition of interstitial magma. Mrcroprobe analyses of apatite show that the columnar apatite has comparatively large Cl content ranging from 0.27 to 0.60 per formula unit based on (O, OH, F, Cl) =26, relative to the needles of apatite (0.08-0.26). There is no significant difference in (F/OH) ratio between the two types of apatite. The columnar apatite with the large Cl content can not considered to have crystallized from Cl-depleted liquid after degassing. It is suggested that dffusive loss of H_2, promoting oxidation of interstitial magma, have preceded the vapor saturation and the resulting degassing process.