This paper describes the mobile control and the standing and sitting motions of an Inverted PENdulum type assistant robot-(I-PENTAR) aiming at the coexistence of safety and work capability. I-PENTAR consists of a body with a high powered waist joint, arms designed for safety, and a wheeled inverted pendulum mobile platform. It is modeled as a three-dimensional robot with controls for inclination angle, linear position, and steering angle, and is controlled by state feedback control based on the LQR method. The motion planning of standing and sitting-important motions for an inverted pendulum type robot in practical use-is proposed. It was experimentally confirmed that I-PENTAR could realize a series of fundamental motions required in practical use, which are standing, running, turning, and sitting stably.