Japanese composer Ishikawa Giichi (1887~1962) transcribed Korean court music repertoires into Western staff notation during the 1930s. An incomplete score of Junggwang-ji-gok (Hyeonak Yeongsan Hoesang) preserved in the National Gugak Center (NGC) has been considered as the only surviving source of these transcriptions by Ishikawa. Recently, however, the TOYAMA Kazuyuki Memorial Archives of Modern Japanese Music, Meiji Gakuin University Library in Tokyo received a donation of Ishikawa’s materials which included previously unknown manuscript transcriptive scores and the other related documents. The Archives also holds two volumes of microfilm donated by music critic Hattori Ryutaro (1900~1977), which was revealed to contain the scores of 27 Korean court pieces transcribed by Ishikawa. This paper investigates the contents of these newly discovered sources within the Ishikawa Collection and microfilms and makes some remarks concerning Ishikawa’s transcription process and his understanding of Korean music as revealed by his transcribing style. According to the donated materials, Ishikawa conducted his transcription work from 1930 until 1935. These materials suggest that he first transcribed the original yuljabo (letter notation designating pitch names) into Western staff notation, and then he checked the scores by comparing them against actual performances by the assistant young musicians of Yiwangjik Aakpu (The Royal Music Institute of Yi Household). The remaining scores, which are theorized to be made in the 1930s, are mostly the part scores for each instrument, whereas the general scores stored on microfilms are instead 1950s (re)writings based on these same 1930s part scores. The microfilms were made in 1962 by the National Diet Library of Japan, although the original manuscripts are currently missing. Ishikawa's scores reflect the notational customs and the actual performance practices of Korean court music in the 1930s: he consistently notated the hwangjong note as C in the same fashion as the other Western-style scores of Korean music at that time; he tried to exactly represent the jangdan (rhythmic/metric cycle) in his scores by using compound and mixed time signatures; and some of the melodic instrumental parts found in pieces like Manp'ajeongshik-ji-gok (Ch'wita) and Junggwang-ji-gok maintain a parallel progression of 4ths, which is never observed in current performance practices. This paper suggests that the NGC version of Junggwang-ji-gok would be an earlier version of Ishikawa's transcriptive scores, written before 1934. This paper also points out that the 1929 manuscript score of Seungpyeongmanse-ji-gok (Yeomillak) preserved in NGC, known as the only surviving transcriptive work by military musician Baek U-yong (1883-1930), was actually notated by Ishikawa, based on the score sharing the same handwriting features as the transcriptions known to be written by Ishikawa himself.