When emitted light from LED 31 is incident on photodiodes 32 and 33 with luminance Pa and Pb, currents ia and ib are generated according to luminance Pa and Pb. When outside light is incident through the finger tissues on photodiodes 32 and 33 with luminance Pc, current ic is produced. The current il (= ia + ic) generated by photodiode 32, and the current i2 (= -ib-ic) generated by photodiode 33, are added at node X, and the current ic corresponding to outside light is thus cancelled. In addition, photodiodes 32 and 33 are disposed at different distances from LED 31. As a result, the current flowing to opamp 34 is current ia corresponding to luminance Pa because luminance Pb is extremely low. The opamp 34 then applies a current voltage conversion to generate pulse wave signal Vm.
