Swimming, one kind of sports and exercises, is very good to health and feasible for all people as well. So far, there is no exercising device for swimming, and the swimming pools are not enough and the available open hours are limited as well. The available time for outdoors swimming pools are dependent on the weather. Therefore, it is very inconvenient for the swimming-lovers to workout by swimming. This study presents a new conceptual design of exercising device for breast stroke swimming. Firstly, calculate the resisting forces of a swimmer during swimming in breast stroke to design the required loading device. Then, design the required mechanism for this novel exercising device which consists of linkages, gears and cams. This design uses SolidWorks software to design all the parts and assemble the whole device. The feasibility of this completed device has been confirmed through the simulation in SolidWorks software and a simple prototype of this device.