A medical tube comprising: a flexible tube-shaped main body; a hub connected to a proximal portion of the tube-shaped main body; and a strain relief supported at a distal portion of the hub, the strain relief surrounding a predetermined range of a proximal side of the tube-shaped main body; the tube-shaped main body includes a flexible portion (30, 40, or 42) whose flexibility for bending is increased by forming at least one groove extending in a circumferential direction in an outer circumferential portion over a predetermined range from a distal side from a most distal portion of the strain relief to a proximal side from the most distal portion, characterized in that a distance from the most distal portion of the strain relief to a most distal portion of the flexible portion (30, 40, or 42) is set to 5 to 50 mm, preferably 10 to 30 mm; and a distance from the most distal portion of the strain relief to a most proximal portion of the flexible portion (30, 40, or 42) is set to 5 to 50 mm, preferably 10 to 30 mm; the medical tube is an introducer sheath indwelled in a lumen of a living body to introduce another elongated medical instrument into the body; a length of the tube-shaped main body is in a range of about 20 to 800 mm; the flexible portion (30, 40, or 42) has higher flexibility than that of the front and rear parts of the flexible portion (30, 40, or 42) in the tube-shaped main body and the flexible portion (30, 40 or 42) has higher flexibility than that of another portion of the tube-shaped main body in which the groove is not provided, that is, a portion on a distal side and a portion on a proximal side from the flexible portion (30, 40, or 42). a flexible tube-shaped main body; a hub connected to a proximal portion of the tube-shaped main body; and a strain relief supported at a distal portion of the hub, the strain relief surrounding a predetermined range of a proximal side of the tube-shaped main body; the tube-shaped main body includes a flexible portion (30, 40, or 42) whose flexibility for bending is increased by forming at least one groove extending in a circumferential direction in an outer circumferential portion over a predetermined range from a distal side from a most distal portion of the strain relief to a proximal side from the most distal portion, characterized in that a distance from the most distal portion of the strain relief to a most distal portion of the flexible portion (30, 40, or 42) is set to 5 to 50 mm, preferably 10 to 30 mm; and a distance from the most distal portion of the strain relief to a most proximal portion of the flexible portion (30, 40, or 42) is set to 5 to 50 mm, preferably 10 to 30 mm; the medical tube is an introducer sheath indwelled in a lumen of a living body to introduce another elongated medical instrument into the body; a length of the tube-shaped main body is in a range of about 20 to 800 mm; the flexible portion (30, 40, or 42) has higher flexibility than that of the front and rear parts of the flexible portion (30, 40, or 42) in the tube-shaped main body and the flexible portion (30, 40 or 42) has higher flexibility than that of another portion of the tube-shaped main body in which the groove is not provided, that is, a portion on a distal side and a portion on a proximal side from the flexible portion (30, 40, or 42).