A controller which generates a driving instruction to control driving of an object while detecting a position of the object based on two periodic signals that are provided by an encoder and have different phases, comprises a counter configured to count periods of one of the two periodic signals, and a processor configured to detect the position of the object based on an arctangent value of a ratio of values of the two periodic signals and a count value provided by the counter, and to generate the driving instruction based on the position, wherein the processor is configured to compensates an error in the count value based on the driving instruction generated in the past and an acceleration of the object computed based on the arctangent value and the count value, and to compute the position of the object based on the compensated count value.