A self-rotation blocking mechanism in a scroll compressor having a movable scroll member and fixed scroll member fixed to a casing. The mechanism is constructed of circumferentially spaced opposing pairs of pins 9 and 10, which are connected to an end plate 12 of the movable scroll member 2 and a faced end wall of the casing 4, respectively, and which are in a side-by-side contacting relationship. The circumferential arrangement of the pins is such that, at every angular position of the movable scroll member, there exists at least one pair of the pins which generates a force in a direction opposite to a self-rotating torque applied to the movable scroll member caused by the compression reaction force. A locally concentrated arrangement of the pairs of the pins for generating such a force can be employed at the angular position which produces a larger value of self-rotating torque. Furthermore, the diameters of the pins are such that one half of the sum of the diameters is equal to or smaller than the radius of the orbital movement of the movable scroll member.