30 which is fixed within first housing portion 11 and orbiting scroll member 40 which is engaged with fixed scroll member 30 orbiting scroll member 40 includes bottom plate 42 spiral element 43 which is formed on a first end surface of bottom plate 42 and boss member 41 which is formed on a second end surface of bottom plate 42 orbiting scroll member 40 is supported on a first end of second housing portion 12 by a rotation preventing mechanism 45 rotation preventing mechanism 45 is comprised of a ball coupling which is disposed around boss member 41 fixed scroll member 30 includes bottom plate 31 spiral element 32 which is formed on a first end surface of bottom plate 31 discharge valve mechanism 33 which is formed on a second end surface of bottom plate 31 and fixed member 34 fixed scroll member 30 is fixed to bottom wall portion 11 a of first housing portion 11 by bolts 54 via fixed member 34 moreover discharge valve mechanism 33 may discharge fluid from motor driven compressor 10 motor 60 is accommodated within space 25 of second housing portion 12 and third housing portion 13 motor 60 is comprised of stator 15 and rotor 16 stator 15 is fixed within housing portions 12 and 13 rotor 16 is mounted to rotary shaft 21 a first end of rotary shaft 21 is rotatably supported by bearing 18 which is disposed within boss member 13 a of third housing portion 13 a second end of rotary shaft 21 includes large diameter portion 21 a large.