In a back massaging apparatus capable of projecting a massaging mechanism forward and returning the same to an original normal position, upon securing a motion amount to be sufficient, the back massaging apparatus is intended to be thinned in the back and forth direction and allow a backrest part as a chair-type massaging machine to be suppressed from thickening. A back massaging apparatus (4) of the present invent ion provided in a chair-type massaging machine (1) includes: a massaging mechanism (10) having: left and right paired massaging members (17) each of which is provided with a treatment unit (21) performing a massaging operation; and a drive unit (18) transmitting a massaging operation to the massaging members (17); a base member (12) which supports the massaging mechanism (10) in a state of the massaging members (17) facing forward; a vertical movement mechanism (13) allowing the base member (12) to move vertically within a backrest part (3); and a projection amount variable mechanism (14) which moves the massaging members (17) so that a projection amount of the treatment unit (21) in the back and forth direction is varied.