In 2000 (Vividharatnakaraṅḋaka. Festgabe für Prof. Mette. Swisttal-Odendorf, pp. 259-281), I published an article in German on the language of the Upaniṡads. The present paper discusses the same topic in Japanese hoping it will benefit my Japanese colleagues, especially those working in Buddhist studies. The article brings to their attention some common features of the language development which can be observed both in the Śvetāśvatara-Upaniṡad and some Buddhist texts. I examine special verbal forms (1., 2.), among them, the present forms used for past events (2.4.), and optative present for the past (also found in the Munḋaka-Upaniṡad) (2.5.), the adverb tatvā (3.), irregular case-forms and meter (4.), meter and phoneme (5.), including tv and hy (5.4.), and declensional irregularities (5.6.). The article contains detailed indexes providing information on the text occurrences and items dealt with, e.g., passages examined, verbal forms, other words, grammatical categories in general, categories of the verbs, phonemes, meters, references to Buddhist Hybrid Sanskrit and Pāli,etc.