A spinal fixation device comprising: a screw part having a screw body part configured to be implanted in a spine; and a head part that is attached to a portion on an opposite side of the screw part to the screw body part and has a slit into which a fixing rod for fixing a plurality of vertebrae (100, 101) is to be inserted, wherein the head part includes: a base part that is provided as a portion on the screw part side of the head part and in which the fixing rod inserted into the slit is held; and a pair of tab parts that are formed so as to extend from the base part to an opposite side to the screw part and face each other across the slit, the pair of tab parts have a tab part-side engagement part to be engaged by an extender-side engagement part that is formed on an extender (10;10a) that is configured to be attached to the pair of tab parts to guide the fixing rod to the slit, a weak part is formed between the base part and the pair of tab parts, the weak part being configured to be broken by an external force from the extender (10; 10a) engaged with the pair of tab parts and separate the pair of tab parts from the base part; and an extender (10; 10a) that is configured to be attached to the pair of tab parts of the spinal implant to guide the fixing rod to the slit formed in the spinal implant, wherein the extender (10; 10a) includes a pair of guide members (11; 11a) that include a pair of main body parts (12; 12b) that are spaced from each other and guide the fixing rod to the slit via a gap between the pair of main body parts (12; 12b) and an extender-side engagement part that is formed on each of the pair of main body parts (12; 12b) to engage with the tab part-side engagement part formed on each of the pair of tab parts of the spinal implant, wherein the main body parts of the extender each include: a base end part that is a portion on an opposite side of the main body part to the extender-side engagement part; and an intermediate part that is a portion of the main body part between the extender-side engagement part and the base end part, the spinal fixation device further comprises an extender guard that is configured to externally cover at least the pair of intermediate parts so as to restrict the pair of guide members from moving closer to or away from each other; the extender guard includes a main body having cylindrical shape, and an inner circumferential surface of the main body includes two groove parts arranged to extend in a longitudinal direction of the main body and to receive the two base end parts and the intermediate parts. a screw part having a screw body part configured to be implanted in a spine; and a head part that is attached to a portion on an opposite side of the screw part to the screw body part and has a slit into which a fixing rod for fixing a plurality of vertebrae (100, 101) is to be inserted, wherein the head part includes: a base part that is provided as a portion on the screw part side of the head part and in which the fixing rod inserted into the slit is held; and a pair of tab parts that are formed so as to extend from the base part to an opposite side to the screw part and face each other across the slit, the pair of tab parts have a tab part-side engagement part to be engaged by an extender-side engagement part that is formed on an extender (10;10a) that is configured to be attached to the pair of tab parts to guide the fixing rod to the slit, a base part that is provided as a portion on the screw part side of the head part and in which the fixing rod inserted into the slit is held; and a pair of tab parts that are formed so as to extend from the base part to an opposite side to the screw part and face each other across the slit, the pair of tab parts have a tab part-side engagement part to be engaged by an extender-side engagement part that is formed on an extender (10;10a) that is configured to be attached to the pair of tab parts to guide the fixing rod to the slit, a weak part is formed between the base part and the pair of tab parts, the weak part being configured to be broken by an external force from the extender (10; 10a) engaged with the pair of tab parts and separate the pair of tab parts from the base part; and an extender (10; 10a) that is configured to be attached to the pair of tab parts of the spinal implant to guide the fixing rod to the slit formed in the spinal implant, wherein the extender (10; 10a) includes a pair of guide members (11; 11a) that include a pair of main body parts (12; 12b) that are spaced from each other and guide the fixing rod to the slit via a gap between the pair of main body parts (12; 12b) and an extender-side engagement part that is formed on each of the pair of main body parts (12; 12b) to engage with the tab part-side engagement part formed on each of the pair of tab parts of the spinal implant, wherein the main body parts of the extender each include: a base end part that is a portion on an opposite side of the main body part to the extender-side engagement part; and an intermediate part that is a portion of the main body part between the extender-side engagement part and the base end part, the spinal fixation device further comprises an extender guard that is configured to externally cover at least the pair of intermediate parts so as to restrict the pair of guide members from moving closer to or away from each other; the extender guard includes a main body having cylindrical shape, and an inner circumferential surface of the main body includes two groove parts arranged to extend in a longitudinal direction of the main body and to receive the two base end parts and the intermediate parts.