The comfort stations were first established at the request of the Japanese military authorities, as part of war efforts in China. According to military documents, private agents first opened brothels for officers and men stationed in Manchuria, around the time of the Manchurian Incident in 1931. Then term "ianfu (comfort women)" was not yet used and the attitude of the military itself was inactive.
When the war spread to Shanghai after the First Shanghai Incident in 1932, the first comfort station was established for a Japanese naval brigade posted there. The number of comfort stations increased rapidly after the Sino-Japanese war broke out in 1937.

It was apparently Yasuji Okamura, at that time the Vice Chief of Staff of the Shanghai Expeditionary Force, who first promoted the establishment of comfort stations for the Japanese army.
There were apparently a number of reasons for establishing them: Japanese military personnel had raped Chinese civilian women in occupied areas on numerous occasions, and the military hoped to prevent a worsening of anti-Japanese feelings on the part of the Chinese people; there was a need to prevent the spread of venereal diseases among officers and men, as otherwise military effectiveness would be reduced; and it was also feared that contact with Chinese civilian women could result in the leaking of military secrets.