SERIAL type not autoincremented

Hello
i have:
create table student(
id                      SERIAL NOT NULL,
name               VARCHAR(35) NOT NULL,
primary key (id)
);

and when i try to insert like this:
insert into student (name) values('me');
i receive error:
ERROR:  duplicate key violates unique constraint "student_pkey"

Why ? Do i understeand correctly that SERIAL == AUTO_INCREMENT ?
As far as i remember i used such type in the past and had no problem.
What do i miss ?

Thanx
Michal