Historical research on labor and gender in Japan is still insufficient. This paper analyzes the notion of gender held by Muto Sanji, who was a prominent business manager in Japan's cotton-spinning industry before WW2. Because the expectations demanded of labor show up in managers' congratulatory messages, we use Muto's congratulatory messages for data. As a result of our analysis, Muto's notion of gender includes (1) a justification of employment using a market-oriented logic, (2) essentialism regarding gender roles in labor, and (3) the justification of a gender division of labor via a genderized family concept. These findings have been overlooked in previous research.