A fluid machine (29A; 29B) comprising: a pump unit or power generating unit (25A; 121) that rotates about a main shaft; an expander that includes a fixed scroll, an orbiting scroll and a rotation restricting mechanism; and a driven crank mechanism that includes: a crankpin that is eccentrically disposed with respect to a larger diameter portion of the main shaft; and an eccentric bush that is inserted in an oscillatable manner with respect to the crankpin and held by a bearing which is disposed on the orbiting scroll, converts between rotational motion of the main shaft and orbiting motion of the orbiting scroll, and is capable of changing an orbiting radius of the orbiting scroll, wherein a first casing including a bearing which supports the larger diameter portion of the main shaft, supports the pump unit or power generating unit (25A; 121) and supports the driven crank mechanism via the main shaft, wherein a second casing (51a; 54) supports the expander, and wherein the first casing and the second casing (51a; 54) are capable of being separated from each other, characterized in that an outer periphery of a fitted portion of the first casing is fitted inside an open end of the second casing (51a; 54), to connect the first casing and the second casing (51a; 54), and a fitting gap between the first casing and the second casing (51a; 54) is sealed with a sealing member (94; 120) disposed on the outer periphery of the fitted portion of the first casing, and when a distance in an axial direction from a tip of the eccentric bush to the sealing member (94; 120) is denoted as A, a distance in the axial direction from an open end edge of the second casing (51a; 54) to an end edge of an opening of the bearing of the orbiting scroll is denoted as B, and a distance in the axial direction from the tip of the eccentric bush to a tip of the fitted portion of the first casing is denoted as C, A > B > C is satisfied. a pump unit or power generating unit (25A; 121) that rotates about a main shaft; an expander that includes a fixed scroll, an orbiting scroll and a rotation restricting mechanism; and a driven crank mechanism that includes: a crankpin that is eccentrically disposed with respect to a larger diameter portion of the main shaft; and an eccentric bush that is inserted in an oscillatable manner with respect to the crankpin and held by a bearing which is disposed on the orbiting scroll, converts between rotational motion of the main shaft and orbiting motion of the orbiting scroll, and is capable of changing an orbiting radius of the orbiting scroll, wherein a first casing including a bearing which supports the larger diameter portion of the main shaft, supports the pump unit or power generating unit (25A; 121) and supports the driven crank mechanism via the main shaft, wherein a second casing (51a; 54) supports the expander, and wherein the first casing and the second casing (51a; 54) are capable of being separated from each other, characterized in that an outer periphery of a fitted portion of the first casing is fitted inside an open end of the second casing (51a; 54), to connect the first casing and the second casing (51a; 54), and a fitting gap between the first casing and the second casing (51a; 54) is sealed with a sealing member (94; 120) disposed on the outer periphery of the fitted portion of the first casing, and when a distance in an axial direction from a tip of the eccentric bush to the sealing member (94; 120) is denoted as A, a distance in the axial direction from an open end edge of the second casing (51a; 54) to an end edge of an opening of the bearing of the orbiting scroll is denoted as B, and a distance in the axial direction from the tip of the eccentric bush to a tip of the fitted portion of the first casing is denoted as C, A > B > C is satisfied.