It is the first recruitment campaign for prison officers in Northern Ireland for more than 20 years.
The new recruits will replace prison officers leaving as part of a redundancy scheme.
So far 371 officers have volunteered to leave and that number is expected to rise by the time applications close on Friday.
There are more than 1,700 prison officers in Northern Ireland and the prison service wants 540 of them to retire early to make way for new recruits on lower salaries.
The redundancy scheme has been introduced for officers aged over 50. Many qualify for a lump sum payment of more than £100,000, plus an annual pension of £18,500.
From Thursday, up to 200 jobs will be available for custody officers, who will be responsible for maintaining security and supervising the movement of prisoners.
Prison officers who take redundancy can apply to be re-employed in the new roles.
But sources say that’s unlikely to happen, because the new jobs won’t be as financially attractive.
On-the-job trainingThe new custody officers will start on a salary of £18,000 – rising to a maximum of £23,000.
The prison officers targeted in the redundancy scheme earn up to £38,000 a year.
Applicants will also have have to pass a number of tests to be short-listed for further assessment, and those appointed will undergo regular on-the-job training and testing to move up the salary scale.
Unlike the Patten reforms of policing, there will not be a 50-50 recruitment process, but advertisements will welcome applications from Catholics, who currently make up 10% of the prison service workforce.
They will also target women, who account for 22% of staff.
The redundancy scheme and recruitment of new staff are key parts of a fundamental programme of reforms for a prison service that has been widely criticised in recent years.
The aim is a new approach as well as new faces.
With Thanks To : By Vincent Kearney BBC NI home affairs correspondent