To obtain a status detector and its status calculation method, capable of obtaining a status quantity in a high response speed, even when the response speed of the status sensor is slow, and obtaining the status quantity, without dispersing even when there is offset in the status speed sensor.

The status detector is provided with a first calculator 34 for calculating difference A between the information of the status speed sensor 1 and the offset correction value, an integrator 31 calculating an integral value by integrating the calculated differential A, a delay filter 32 for calculating the filter value identical to the response delay of the status sensor 1 for the integrated value, a second calculator 35 for calculating difference B between the filter value and the information of the status sensor, and a third calculator 32 for producing a status quantity detection value 4 by making product of the differential B and the gain as the offset correction value and subtracting the difference B from the integrated value.