rate setting unit 220 receives the count value and determines whether the value is more than a predetermined threshold value if it is determined that the value is equal to or less than the threshold value u2018 no u2019 in step s 310 the abnormality removing process ends if it is determined that the value is equal to or more than the threshold value u2018 yes u2019 in step s 310 the process proceeds to step s 320 that is after a second predetermined time has elapsed in step s 310 the process proceeds to step s 320 in addition a timer different from that in the first embodiment not the counter may be used to determine whether the second predetermined time has elapsed in step s 320 the low pass filtered flow rate setting unit 220 sets the current high frequency flow rate eh to the high frequency low pass filtered flow rate fh and the current low frequency flow rate el to the low frequency low pass filtered flow rate fl since the current high frequency flow rate eh and the current low frequency flow rate el have substantially the same value the absolute value of the difference between the set low frequency low pass filtered flow rate fl and the set high frequency low pass filtered flow rate fh is less than the comparison value therefore the determination result of step s 210 which will be performed after this process is u2018 yes u2019 and the abnormal state is removed in step s 250 after a.