To provide a magnetic recording mechanism for a passbook which can ensure data write positioning accuracy regardless of passbook specifications.

The magnetic recording mechanism for a passbook is provided with a horizontal magnetic stripe reading/writing mechanism which is attached to a first reference passbook in which one side of a passbook 31 brought into contact with a carrying reference plane 21 formed on one side of a carrying path of the passbook is made an arrangement reference of a magnetic stripe and reads and writes a horizontal magnetic stripe formed in a direction perpendicular to a carrying direction, and a vertical magnetic stripe reading/writing mechanism which is attached to a second reference passbook in which the other side of the passbook brought into contact with a wide guide 51 formed on the other side of the carrying path of the passbook is made an arrangement reference of the magnetic stripe and reads and writes a vertical magnetic stripe 32 formed in a direction parallel with the carrying direction, wherein the wide guide presses the second reference passbook to the carrying reference plane side in interlock with a magnetic head for reading and writing the vertical magnetic stripe attached to the second reference passbook.