We propose a mobile robot helper and its motion control algorithm for handling an object in cooperation with a human. First, we introduce a prototype of the mobile robot helper, "MR Helper", which consists of two manipulators and an omnidirectional mobile base. We then propose a control algorithm of the MR Helper for handling an object in cooperation with a human. The control algorithm specifies the apparent dynamics of the manipulated object so that the human could handle the manipulated object together with the robot. Load sharing by the MR Helper and a human is also realized by introducing a lifting-up/down system. The control algorithm is experimentally applied to the "MR Helper", and the experimental results illustrate the validity of the proposed control algorithms.