Ten-year (1987--1996) summertime simulations are conducted using a regional climate model to investigate the impact of tropical cyclones on simulated summertime circulation over east Asia. Toward this end, a tropical cyclone-bogusing scheme is incorporated into a regional climate-modeling framework to realistically describe tropical cyclone structure and its intensity during seasonal integration. The simulated summertime monsoon climatology with and without bogus tropical cyclones incorporated into the large-scale forcing of the NCEP/NCAR reanalysis is analyzed. The model with the bogus tropical cyclones shows improvement in the intensity and tracks of the tropical cyclones. In addition, the well-defined tropical cyclones in the model are sustained for a longer time, so they actually modify the east Asian summer monsoon circulation as well as the extratropical circulation. The bogus tropical cyclones in the model also produce much stronger convection and then a larger amount of precipitation modifying the entire precipitation pattern. Meanwhile, compared with the observations, the intensity of the bogus tropical cyclones weakens more rapidly in the earlier stage of the tropical cyclone development. With the bogus tropical cyclones, the large-scale features over east Asia are closer to observations. Major results are as follows: (1) The intensity of the North Pacific subtropical high becomes weaker, while it is excessively intensified and shifted northward without the bogus tropical cyclones. (2) The southerly or southwesterly monsoon flows in the lower troposphere are reduced, meanwhile they are too strong, accompanying the northward excessive transport of moisture in the no-bogus simulation. (3) The midlatitude jets and storm tracks are intensified and shifted southward. (4) Especially, the retreat of the east Asian summer monsoon in late August is well reproduced, which is completely missed in the cases of poorly resolved tropical cyclones. (5) The empirical orthogonal function analysis reveals that the large-scale variability of the east Asia summertime circulation does appear realistically with the bogus tropical cyclones. (6) The biweekly period related to the life cycle of the intraseasonal monsoon depressions is much weakened, while the period of 5 ~ 7 days associated with the synoptic or mesoscale disturbances, such as tropical cyclone activities, is intensified. One of the important findings in this study is that with the bogus tropical cyclones, the secondary rainy season in late August associated with the retreat of the east Asian summer monsoon is simulated realistically. The secondary rainy season annually takes place in middle-latitude east Asia, especially over southern China, Korea, and Japan. This finding strongly suggests that one of the major reasons for the secondary rainy season could be tropical cyclone activities.