A positioner (200, 200D) comprising: a control calculating portion adapted to receive, as inputs, an opening setting signal (Xsp) for a valve, sent from a higher-level device, and an actual opening signal (Xpv) expressing the current opening of the valve, and adapted to generate a control signal from the opening setting signal and the actual opening signal; an electropneumatic converting portion adapted to convert the control signal from the control calculating portion into an air pressure (Pn); a pneumatic circuit portion adapted to use, as an input air pressure, the air pressure (Pn) that has been converted by the electropneumatic converting portion, for amplifying this input air pressure to form an output air pressure, and adapted to output this output air pressure to the valve; a valve opening detecting portion adapted to detect the current opening of the valve to produce an actual opening signal (Xpv) for the control calculating portion; a first calculating portion and a second calculating portion, which structure the control calculating portion; a first pressure sensor adapted to detect an output air pressure from the pneumatic circuit portion at the valve; a second pressure sensor adapted to detect an output air pressure from the pneumatic circuit portion to the valve or an input air pressure from the electropneumatic converting portion to the pneumatic circuit portion; a first case that contains the first calculating portion, the valve opening detecting portion, and the first pressure sensor; and a second case that contains the second calculating portion, the electropneumatic converting portion, the pneumatic circuit portion, and the second pressure sensor, wherein: the first case is to be assembled together with the valve; the second case is to be located in a position away from the valve; the first calculating portion is adapted to receive, as inputs, the opening setting signal (Xsp) that is sent from the higher-level device, the actual opening signal (Xpv) that is sent from the valve opening detecting portion, and a detected pressure signal from the first pressure sensor; and the second calculating portion is adapted to receive, as inputs, an output signal from the first calculating portion, and a detected pressure signal from the second pressure sensor. a control calculating portion adapted to receive, as inputs, an opening setting signal (Xsp) for a valve, sent from a higher-level device, and an actual opening signal (Xpv) expressing the current opening of the valve, and adapted to generate a control signal from the opening setting signal and the actual opening signal; an electropneumatic converting portion adapted to convert the control signal from the control calculating portion into an air pressure (Pn); a pneumatic circuit portion adapted to use, as an input air pressure, the air pressure (Pn) that has been converted by the electropneumatic converting portion, for amplifying this input air pressure to form an output air pressure, and adapted to output this output air pressure to the valve; a valve opening detecting portion adapted to detect the current opening of the valve to produce an actual opening signal (Xpv) for the control calculating portion; a first calculating portion and a second calculating portion, which structure the control calculating portion; a first pressure sensor adapted to detect an output air pressure from the pneumatic circuit portion at the valve; a second pressure sensor adapted to detect an output air pressure from the pneumatic circuit portion to the valve or an input air pressure from the electropneumatic converting portion to the pneumatic circuit portion; a first case that contains the first calculating portion, the valve opening detecting portion, and the first pressure sensor; and a second case that contains the second calculating portion, the electropneumatic converting portion, the pneumatic circuit portion, and the second pressure sensor, wherein: the first case is to be assembled together with the valve; the second case is to be located in a position away from the valve; the first calculating portion is adapted to receive, as inputs, the opening setting signal (Xsp) that is sent from the higher-level device, the actual opening signal (Xpv) that is sent from the valve opening detecting portion, and a detected pressure signal from the first pressure sensor; and the second calculating portion is adapted to receive, as inputs, an output signal from the first calculating portion, and a detected pressure signal from the second pressure sensor. the first case is to be assembled together with the valve; the second case is to be located in a position away from the valve; the first calculating portion is adapted to receive, as inputs, the opening setting signal (Xsp) that is sent from the higher-level device, the actual opening signal (Xpv) that is sent from the valve opening detecting portion, and a detected pressure signal from the first pressure sensor; and the second calculating portion is adapted to receive, as inputs, an output signal from the first calculating portion, and a detected pressure signal from the second pressure sensor.