CURRENT FLOW METER

PURPOSE:To obtain an accurate current flow speed by detecting an orientation error of an orientation sensor and an error of the speed in reference to the ground by referring to a speed in reference to the ground besides that in reference to the ground/water. CONSTITUTION:A speed for the ground and that for water are detected by an operation portion 31 of speed in reference to the ground/water of a current-flow meter 3 based on an orientation which is detected by an orientation sensor 1. If this detected speed in reference to the ground is normal, the speed in reference to the ground is input to a current-flow operation portion 32 through a selection switch 6. The speed in reference to the ground and its orientation are also detected in an navigation method device 4 in parallel with detection by the current-flow meter 3. The orientation error angle is obtained by an orientation error operation portion 7 based on the speed in reference to the ground and the orientation which are detected by the current-flow meter 3 and the device 4. When any abnormality occurs during detection of the speed in reference to the ground by the current-flow meter 3 and the speed in reference to the ground cannot be detected normally, the abnormality is judged by a signal judgment portion 5, selection switches 6 and 9 are switched, and the speed in reference to the ground which is detected by the device 4 is input to the operation portion 32.