Seodang Lee, Deok-Su (1673～1744), from the family that passed the civil service exams for five successive generations, had successively filled Daejehak positions for many years in the Yeongjo era of the Joseon Dynasty. He was famous of extensive reading to mention that he had read three thousand books until the age of 18 and seven to eight thousand books for 40 years after that. His writings include 『Seodang Sajae』, 『Seokgalrok』, 『Pajorok』 etc. The 『Pajorok』 and 『PajoSokrok』 contain his reading, knowledge and meditation in his old age, and in particular, the 『PajoSokrok』 is first introduced by this article. The two books have many reviews on 『Noja (Lao-tzu)』, 『Jangja (Chuang-tzu)』, Bulgyeong and Yeokgyeong, and the expression of opinions on human nature and self-discipline. The discussions in this thesis are as followings;Lee, Deok-Su found the human mind precarious as it was in '16-ja Simbeop' and attempted to approach 'the mind' of the ancient people via bookreading. Besides he preferred the Simseongron (the theory of mind and nature) of Taoism and Buddhism, which briefly pointed out the reasons, to that of Confucian that simply focused on Janggu writing style. This is more evident in the discussion of comparison between the Simseongron of Confucian and that of Taoism / Buddhism and he traced the origin of the institutes of Manse Simhak which was referred to as Jeong (靜) and Heo (虛), in Lao-tzu and Buddhism. Lee had studied Yeokhak in his old age, by researching on Seoncheon Yeokhak which was represented by Hadorakseo(河圖洛書) and Bangwondo(方圓圖), not on Yili-yi of Confucian. He determined that Seoncheonyeok was originated from Jin Dan, the teacher of Taoism and So Ong learned and succeeded it, and which led to the interest in Seo, Gyeong-Deok who was called So Ong of Joseon. So Ong's Seoncheonyeok, so-called Simhak, viewed concentrating the whole mind as 'the key of simhak'. In this respect, Lee's Seoncheonyeok is also an extension of Simhak. In conclusion, Lee found the major means of Simhak in bookreading rather than in gyeokmul (investigation of things) of Confucian or chamseon (Buddhist meditations) of Bulga, and he continued the tradition of Seoncheon Simhak(先天心學) that had been led by Jin Dan, So Ong and Seo, Gyeong-Deok based on the Simhak of Taoism and Buddhism.