There is a political movement to extension of a voluntary part-time work for improvement of employment-population ratio by the government. Traditionally, a part-time work has been recognised as the transition way to get a full-time job or the method to balance job and family for working women. As times change, there are a lot of demand for finding a part-time work with various reasons. Nevertheless, the legislations related to employment and labour relations seem to presume that a general-type of an employee is a full-time worker. The anti-discrimination procedure for irregular workers has been introduced to resolve this problems since 2006 (there was not a lot in between). In these circumstances, this article trys to find a way for extension of a voluntary part-time worker in perspective on Labour Law. The article deals with two substantive matters, one is flexible work in employment and the other is the anti-discrimination procedure. There are two types of a part-time work, new hiring part-time work and the converted one from a full-time worker, and the latter could be in the true sense of a voluntary part-time work. To promote a part-time work and to realise work-family balance, the Equal Employment and Work-Family Balance Assistance Act(EWBA) provides a flexible working system. The problem is that there are a lot of ways to get around the regulations for employer and there is no method to guarantee the effectiveness of that. To make better use of the system, it should be changed when a full-time worker asks an employer to transpose into a part-time worker, the legal obligation of an employer should be established for consultation and agreement. Moreover, the boundaries of claim for a part-time work should be extended in a full-time employee who has to do family care. To improve the effectiveness of the anti-discrimination procedure for a part-time worker, the regulations about the prerequisite should be changed for the applicant and the comparator requirement to promote the claim as well as systematic changes to beef up professionalism to judge discrimination in employment. The limited right for equal treatment in the regulations does little to confront the problems. In order to bring about the genuine transformation of a part-time work, the focus should be on the protection of their rights.