A measuring method wherein: a physical quantity is measured by a measuring device in a main process that is repeated with a period of a process time t 0 having a prescribed length, the measuring device is activated only for a measurement time t 1 that is shorter than the process time t 0 to measure the physical quantity and is deactivated during a deactivated time t 2 in the main process, a relationship among t 0, t 1, t 2 is expressed by a formula, t 0 = t 1 + t 2, a temporal variation in a measured value of the physical quantity measured by the measuring device is a drift, a temporal variation in the measured value after activation of the measuring device is an activation drift, and a temporal variation in the measured value after deactivation of the measuring device is a deactivation drift, the measuring method is executed using a graph a indicating an activation drift characteristic of the measuring device, a graph b indicating a deactivation drift characteristic of the measuring device, and a prescribed allowable measurement error, and the measuring method includes a step of determining a section in which the activation drift is equal to or smaller than the allowable measurement error within a range of the measurement time t 1, from the graph a, a step of determining a section in which the deactivation drift is equal to or smaller than the allowable measurement error within a range of the deactivation time t 2, from the graph b, and a step of adjusting a warm-up time (t D) from activation of the measuring device to start of measurement so that the process time t 0 that is expressed by t 1 + t 2 becomes equal to a prescribed value. a physical quantity is measured by a measuring device in a main process that is repeated with a period of a process time t 0 having a prescribed length, the measuring device is activated only for a measurement time t 1 that is shorter than the process time t 0 to measure the physical quantity and is deactivated during a deactivated time t 2 in the main process, a relationship among t 0, t 1, t 2 is expressed by a formula, t 0 = t 1 + t 2, a temporal variation in a measured value of the physical quantity measured by the measuring device is a drift, a temporal variation in the measured value after activation of the measuring device is an activation drift, and a temporal variation in the measured value after deactivation of the measuring device is a deactivation drift, the measuring method is executed using a graph a indicating an activation drift characteristic of the measuring device, a graph b indicating a deactivation drift characteristic of the measuring device, and a prescribed allowable measurement error, and the measuring method includes a step of determining a section in which the activation drift is equal to or smaller than the allowable measurement error within a range of the measurement time t 1, from the graph a, a step of determining a section in which the deactivation drift is equal to or smaller than the allowable measurement error within a range of the deactivation time t 2, from the graph b, and a step of adjusting a warm-up time (t D) from activation of the measuring device to start of measurement so that the process time t 0 that is expressed by t 1 + t 2 becomes equal to a prescribed value.