A tape guide mechanism in a magnetic recording and reproducing apparatus is provided; the magnetic recording and reproducing apparatus includes a movable chassis 1 having a tape guide arm member 30 on which a tape guide 31 is erected and a pair of reels stands thereon and a fixed chassis 2 having a magnetic rotary head thereon, in which the movable chassis 1 moves to one position of said fixed chassis 2 to perform loading and unloading of a cassette and when moves to the other position, tape loading of taking out a magnetic tape from the reel of the loaded cassette to be wound around the magnetic rotary head is performed, wherein after completing the tape loading, the tape guide 31 is fixed to a predetermined position by a guide receiving member 40 that is provided on the fixed chassis 2 to receive the tape guide 31, and in the middle of the tape guide 31 traveling to said predetermined position, the tape guide arm member 30 is made to move along a groove 2a provided in the fixed chassis 2 to determine the position in the chassis plane direction and is guided and moved by the projections 36 provided on the lower surface of the tape guide arm member 30 to determine the position in the height direction.