This paper reports on the continued development of a new concept for a personal vehicle called the 'Personal riding-type wheeled Mobile Platform (PMP)' that consists of two wheels and a standing base for a human rider. The two wheels are driven independently, and forward and backward movement and steering are achieved by simply changing the relative position of the rider's center of gravity (COG) on the base. The vehicle has two distinct advantages: a reduction in total weight through its simple structure and a space-saving design that does not use a steering unit. We have already proposed the first prototype (PMP-1) and its posture stabilizing and running control methods, and we have achieved proper forward and backward movement according to the rider's intentions. This paper describes our proposed structure for detecting the rider's COG on the base and the steering control method in order to achieve steering control by changing the position of the rider's COG. and the second prototype (PMP-2) whose weight is smaller than 12kg. We also investigated the steering control method to improve maneuverability in various estimated standing poses. Our experimental results demonstrate that natural steering control can be achieved using the rider's COG based on the rider's intentions.