A safety belt for coupling respective upper body parts of a driver of a two-wheeled vehicle and a passenger thereof, characterized by comprising: a tabular first backing member attached to a back of the driver; a first waist belt (a2, a3) coupled to a lower part of the first backing member and attached around a waist of the driver; a pair of first shoulder belts (a4, a5) coupled to an upper part of the first backing member and attached around shoulders of the driver; a second waist belt attached around a waist of the passenger and having front portions located at the driver side detachably inserted in a width direction of the first backing member in a waist belt attaching portion provided on the first backing member or caught by the waist belt attaching portion in a manner spaced apart from each other at a predetermined clearance in the width direction of the first backing member; a pair of second shoulder belts (b3, b4) attached around shoulders of the passenger and having respective front portions located at a driver side detachably attached to a shoulder belt attaching member provided on the first backing member in a manner spaced apart from each other at a predetermined clearance in the width direction of the first backing member at a location above the position of the waist belt attaching portion, wherein a plurality of waist belt attaching portions (a10, a11, a12) are provided on the first backing member in a manner spaced apart from one another in a vertical direction, and a plurality of shoulder belt attaching members (a6, a7, a8, a9) are provided on the first backing member in a manner spaced apart from each other in the vertical direction, and an attachment position of the second waist belt and attachment positions of the second shoulder belts are selectable accordingly among the plurality of waist belt attaching portions and the plurality of shoulder belt attaching members. a tabular first backing member attached to a back of the driver; a first waist belt (a2, a3) coupled to a lower part of the first backing member and attached around a waist of the driver; a pair of first shoulder belts (a4, a5) coupled to an upper part of the first backing member and attached around shoulders of the driver; a second waist belt attached around a waist of the passenger and having front portions located at the driver side detachably inserted in a width direction of the first backing member in a waist belt attaching portion provided on the first backing member or caught by the waist belt attaching portion in a manner spaced apart from each other at a predetermined clearance in the width direction of the first backing member; a pair of second shoulder belts (b3, b4) attached around shoulders of the passenger and having respective front portions located at a driver side detachably attached to a shoulder belt attaching member provided on the first backing member in a manner spaced apart from each other at a predetermined clearance in the width direction of the first backing member at a location above the position of the waist belt attaching portion, wherein a plurality of waist belt attaching portions (a10, a11, a12) are provided on the first backing member in a manner spaced apart from one another in a vertical direction, and a plurality of shoulder belt attaching members (a6, a7, a8, a9) are provided on the first backing member in a manner spaced apart from each other in the vertical direction, and an attachment position of the second waist belt and attachment positions of the second shoulder belts are selectable accordingly among the plurality of waist belt attaching portions and the plurality of shoulder belt attaching members.