For the prevention of COVID-19, many companies have been forced to adopt telework. There is mixed evidence showing that telework increases work-family conflict and, conversely, that it brings harmony between work and family. Little is known about how workers who transmitted to telework from on-site work responded in this unique circumstance of COVID-19 pandemic in Japan. Results of an online survey using a crowdsourcing service (N = 1,412) demonstrated that workers with a higher percentage of transition to telework had higher levels of family interference with work, while no significant effect on work interference with family or stress. In addition, there was no significant moderating effect of participants’ gender or the age of their youngest child on these relationships. These results suggest that the transition to telework have increased work-family conflict during COVID-19 pandemic in Japan.