To provide an amidite for nucleic acid synthesis, which enables a protective group therein to be removed under moderate conditions and can be practically used, and a nucleic acid synthesizing method using the amidite for nucleic acid synthesis. Specifically, the present invention relates to an amidite for nucleic acid synthesis represented by General Formula (I) below, and a nucleic acid synthesizing method using the amidite for nucleic acid synthesis: where X denotes a base; Y denotes a protective group formed of any one of a 4-aminobutyric acid derivative, an o-aminomethylbenzoic acid derivative, an o-aminophenylacetic acid derivative, an o-aminoethylbenzoic acid derivative, an o-aminomethylphenylacetic acid derivative, an o-aminophenylpropionic acid derivative and a 5-aminovaleric acid derivative; and Q denotes one of a hydrogen atom and a hydroxyl group.