This study was conducted with the aim of developing and validating a measure of the workplace bullying bystander behavior. To this end, items were developed by referring to previous studies related to workplace bullying, and subtypes were defined as pro-bullying, defending, and outsider behaviors. After confirming the validity of the content with the help of experts, a total of 31 preliminary items were composed. The final 26 questions were selected by conducting exploratory factor analysis with a survey of 288 office workers who have directly or indirectly witnessed workplace bullying over the past three years, and in this process, it was confirmed that defense behavior was distinguished into two types: Active and supportive. Confirmatory factor analysis was conducted with data from 518 office workers who have directly or indirectly witnessed workplace bullying over the past year, and the validity and reliability of the developed scale were confirmed. As a result of comparing the competing models to reconfirm the subtypes, it was confirmed again that active defense behavior and supportive defense behavior were distinguished. The criterion-related validity of all subtypes was confirmed by setting the criteria variables for workplace bullying behavior, altruistic behavior, pro-social behavior, fear of intervention, moral disengagement, guilt, and moral identity. Based on the result of this study, follow-up research tasks related to workplace bullying bystander behavior scale were suggested and the methods to prevent and intervene in workplace bullying utilizing workplace bullying bystander behaviors were discussed.