Parent–child interaction therapy (PCIT) is an empirically supported behavioral parenting intervention developed for families with young children who have significant behavior problems. In Japan, PCIT was introduced in 2008 as a parenting intervention method and later introduced to therapists. This case study reports on the detailed use of PCIT, originally developed in Western cultures, for a 5-year-old Japanese boy with behavioral problems and his mother. During the treatment, the mother successfully acquired PCIT skills in the early stages of the coach sessions that led to improvements in the child’s problematic behavior. However, especially in the later stages of the treatment, the mother was too tired/distressed to focus on the treatment, which complicated the implementation of PCIT (e.g., unable to do homework, canceled sessions). This was mainly because she was a full-time working mother who was very busy with work, housework, and child-rearing, and also had no help from her husband. Cases such as this are commonly seen in current Japanese society. In summary, this case study supported the potential effectiveness of Western-originated PCIT for Japanese families with children who have behavioral problems, and also argued that there is a need for PCIT therapists to carefully assess and address the primary caregiver’s distractions outside the session room especially when working with Japanese working mothers.