Abstract: To provide an air injection device for a dental handpiece which makes it possible to obtain a clear image even if the position of an image taking part is changed, provided is an air injection device including: a trunk connector (41) that is in a form of a column, in the trunk connector a passage being formed; an air guiding pipe (45) that is in a form of a pipe, one end of the air guiding pipe being connected to the trunk connector, the air guiding pipe having flexibility; and a means (46) that retains the air guiding pipe in the dental handpiece main body, wherein the passage in the trunk connector branches, one of the branching passages communicating with the air guiding pipedental handpiece.