Abstract: The present invention relates to a spatial cam power transmitting mechanism for the conversion between linear movement and rotary motion. Several transmitting mechanisms for the conversion between reciprocating motion of a roller shaft and rotary motion of an internal groove cam are provided, which do not have a piston and a piston bore. A roller shaft 16 is provided on a upper portion of internal groove cam 6 in a cam casing 15, and rollers are mounted to the outer end of the roller shaft. The rollers roll in a circumferential direction on the contour line of the groove of the internal groove cam 6. At the position of fixed rails 4 opposing to the roller shaft 16, guiding rollers or slide blocks 27 are provided, wherein the fixed rails 4 are provided axially in a lower portion of a cover 1 of the cam casing. The guiding rollers or slide blocks 27 can move up and down respectively in the fixed rails.