PURPOSE: To eliminate or reduce the leakage of a signal by additionally installing a switch on a parallel signal and separating a high impedance node reading a serial signal and the intersection part of parallel signals by means of said switch.

CONSTITUTION: Two write switches 2-i-1 and 2-o-2 are installed so as to sandwich a signal output wiring 7 and the intersection part of parallel input signals. Where the size of a parasitic capacity between a read output terminal 7 and a negative input terminal 5, and the size of a capacitor 3-i are c1 and ci, respectively, a voltage read during a read period is lower than a sampled and held input signal voltage ein1. In order to avoid said error, a write switch 2-i-1 near the capacitor is also installed, thereby eliminating the influence of the parasitic capacity 11-j. Namely, two switches are installed on a parallel signal wiring intersecting the serial output signal so as to sandwich the intersection part, whereby a parallel/serial conversion circuit insuring a parallel signal against leaking to a serial signal can be formed at high accuracy.