To provide an active image sensor capable of sharing one set of read circuits by the photodiodes of two active image sensors in contact with each other.

The active image sensor provided with a shared read structure is provided with a first photodiode D1, a first NMOS transistor M1, a second photodiode D2, a second NMOS transistor M2, a third NMOS transistor M3 and a fourth NMOS transistor M4. By time division controlling the changeover of first and second selection signals are reset signals and switching the potential of a variable voltage source, luminosity sensed by the first and second photodiodes D1, D2 is read from an output end present at the source of the fourth NMOS transistor M4.