This study identified coworkers’ attitudes toward long-term parental leave for men. Twelve male enterprise workers were interviewed using a semi-structured format. These employees knew male coworkers who had taken parental leave for a minimum of one month. The data collected were analyzed using a modified grounded theory approach (M-GTA), and 11 categories and 35 concepts were generated. The findings reveal the following. (a) The support for male parental leave is promoted by a conducive work environment and is mutually influenced by a sense of mutual support in the workplace. (b) Even if a worker initially supports male parental leave, a sense of unfairness and negative feelings due to excessive workload gradually diminish the support for male parental leave, leading to conflicts over male parental leave. Finally, (c) negative feelings about taking over the work and excessive workload contribute to a sense of unfairness.