A liquid medicine injection device comprising: a casing (110, 150): a button exposed outside the casing (110, 150); a needle holder located in the casing (110, 150) and coupled to a needle; a spring located in the casing (110, 150) and interposed between the button and the needle holder; and a guiding member located in the casing (110, 150) to support the needle holder, wherein the needle holder is provided to rotate by an operation of the button, wherein the device further comprises a guide wall, wherein the guiding member is provided on an inner surface of the guide wall, and the needle holder comprises: a first support supported by the guiding member in a first state; and a guiding groove provided to be adjacent to the first support and to pass the guiding member therethrough in a second state where the needle holder is rotated from the first state, wherein the guiding member comprises a second support provided to support the first support in the first state, wherein the guiding groove is provided to pass the second support therethrough in the second state, wherein in the first state, the first support of the needle holder contacts and supports the second support of the guiding member, and wherein the first support comprises: a support groove formed at a surface facing an insertion direction of the needle and connected to the guiding groove; and a support stopper located between the support groove and the guiding groove to provide a resistance to the rotation of the needle holder. a button exposed outside the casing (110, 150); a needle holder located in the casing (110, 150) and coupled to a needle; a spring located in the casing (110, 150) and interposed between the button and the needle holder; and a guiding member located in the casing (110, 150) to support the needle holder, wherein the needle holder is provided to rotate by an operation of the button, wherein the device further comprises a guide wall, wherein the guiding member is provided on an inner surface of the guide wall, and the needle holder comprises: a first support supported by the guiding member in a first state; and a guiding groove provided to be adjacent to the first support and to pass the guiding member therethrough in a second state where the needle holder is rotated from the first state, wherein the guiding member comprises a second support provided to support the first support in the first state, wherein the guiding groove is provided to pass the second support therethrough in the second state, wherein in the first state, the first support of the needle holder contacts and supports the second support of the guiding member, and wherein the first support comprises: a support groove formed at a surface facing an insertion direction of the needle and connected to the guiding groove; and a support stopper located between the support groove and the guiding groove to provide a resistance to the rotation of the needle holder. a first support supported by the guiding member in a first state; and a guiding groove provided to be adjacent to the first support and to pass the guiding member therethrough in a second state where the needle holder is rotated from the first state, wherein the guiding member comprises a second support provided to support the first support in the first state, wherein the guiding groove is provided to pass the second support therethrough in the second state, wherein in the first state, the first support of the needle holder contacts and supports the second support of the guiding member, and wherein the first support comprises: a support groove formed at a surface facing an insertion direction of the needle and connected to the guiding groove; and a support stopper located between the support groove and the guiding groove to provide a resistance to the rotation of the needle holder. a support groove formed at a surface facing an insertion direction of the needle and connected to the guiding groove; and a support stopper located between the support groove and the guiding groove to provide a resistance to the rotation of the needle holder.