Position measurement apparatus

A relative position identifying unit 221 identifies a relative position of a scale 111 to a light receiving unit. An absolute position identifying unit 141 identifies an absolute position of the scale111 at a timing of execution of a synchronization instruction. A determining unit 241 determines a measurement reference position based on the absolute position at the timing and the relative position at the timing. A current position calculator 242 calculates a current position of the scale 111 based on the measurement reference position and the relative position identified by the relative position identifying unit 221. A control unit 240 as a synchronization instructing unit executes the synchronization instruction on the absolute position identifying unit 141 and the determining unit 241. 相对位置识别单元221识别标尺111对于光接收单元的相对位置。绝对位置识别单元141在执行同步指令的定时识别标尺111的绝对位置。确定单元241基于所述定时的绝对位置和该定时的相对位置来确定测量参考位置。当前位置计算器242基于测量参考位置和由相对位置识别单元221识别的相对位置来计算标尺111的当前位置。作为同步指令单元的控制单元240对绝对位置识别单元141和确定单元241执行同步指令。