Disclosed is a stirring tool which is capable of fully and efficiently mixing ingredients such as mayonnaise even in relatively small amounts. The remainder of each log is attached to the succeeding log. Values of the time difference are calculated for the measurement messages transmitted in at least one of the transmission directions, each of which values is the difference between the instant of reception measured at the reception and the instant of transmission measured at the transmission of the measurement message. The controller may be configured to selectively reduce an amount of fluid displaced during at least one, but less than all of the plurality of displacement strokes. The secondary cell module is of a simple structure and it can be small-sized and light-weighted or thin-shaped as necessary and the heat which generates inside the cell can be efficiently diffused to outside, thereby enabling the production of cells of high capacity with a high degree of freedom in designing its shape as well as supreme productivity.