Helicity-dependent photocurrent ΔI has been detected successfully under experimental configuration that a circularly polarized light beam is impinged with a right angle on a cleaved sidewall of the Fe/x-AlO_x/GaAs-based n-i-p double-heterostructure. The photocurrent ΔI has showed a well-defined hysteresis loop which resembles that of the magnetization of the in-plane magnetized Fe layer in the devices. The value of ΔI with a shunt resistance of 10 kΩ has been |ΔI| ～0.2 nA at 5 K under the remnant magnetization state. Study on temperature dependence of the relative ΔI value at H = 0 has revealed that it is maximized at temperatures 125 ― 150 K, and is still measurable at room temperature.