The motion of particles caused by a single bubble which is blown into a two-dimensional fluidised bed has been studied. A drift line which is shown when a bubble has passed through the bed is obtained as a generalized curve. The experimental results can be explained fairly well by the authors' model. The model is as follows. 1. The motion of particles is assumed as the motion of perfect fluid caused by the motion of a circular cylinder in the perfect fluid. 2. There is an imaginary wall at the distance of the diameter of bubble below from the center of the moving bubble and it moves upwards with the same velocity as the bubble
