A shield machine according to the present invention includes: a body (1) having an oval cross section; a circular plate member (17) mounted on a front end-side portion of a shield machine main body (3); a first rotating mechanism (18) which rotates the circular plate member (17); a pair of pivot arms (19) which are rotatably supported by the circular plate member (17); a pair of second rotating mechanisms (20) which rotate the pair of pivot arms (19); a pair of head supporting members (19a) which are firmly fixed to tip end portions of the pivot arms (19); a pair of rotary cutter heads (4) which are rotatably mounted on the head supporting members (19a) and each of which has a diameter that is half a short diameter of the oval cross section of the body; and a pair of third rotating mechanisms (21) which rotate the rotary cutter heads (4) around third center axes.