In a position-direction measuring apparatus that is in principle incapable of determining a true position among two positions which are point symmetrical with respect to a certain point, the invention intends to reduce the possibility of an error and to enable arbitrary setting of the hemisphere at the start of measurement. Light is imaged by collecting light, converting the collected light into a electrical charge signal, multiplying the electrical charge signal to produce multiple electrical charge signals with associated levels of gain, converting the electrical charge signals to voltage signals, and developing an output signal from one or more of the voltage signals that represents the collected light. 1 measured at each of wavelengths of 215 nm, 280 nm and 320 nm with respect to a 0.