A method for producing a modified conjugated diene-based polymer that produces a modified conjugated diene-based polymer that is a modified product of a conjugated diene-based polymer obtained by polymerizing a conjugated diene compound, or polymerizing a conjugated diene compound and an aromatic vinyl compound, in the presence of an alkali metal compound or an alkaline-earth metal compound, the method comprising: a main chain modification step that reacts at least either an unsaturated bond or a functional group that is included in the conjugated diene-based polymer and is not situated at a terminal of the conjugated diene-based polymer, with a specific compound that includes a functional group that interacts with silica, the main chain modification reaction being performed against a terminal-modified polymer or being performed simultaneously with a terminal modification reaction that modifies the terminal of the conjugated diene-based polymer,_the terminal-modified polymer being obtained by introducing a functional group that interacts with silica into at least one terminal of the conjugated diene-based polymer wherein the specific compound is at least one compound selected from a group consisting of a compound (a-1) represented by a formula, and a compound (a-2) that includes a functional group and a group in its molecule, the functional group being at least one functional group selected from a group consisting of a cyclic ether group and a (thio)carbonyl group, and the group including at least one atom selected from a group consisting of a nitrogen atom, a phosphorus atom, an oxygen atom, and a sulfur atom, and not including active hydrogen, the group differing from the functional group, wherein A 1 is a monovalent functional group that includes at least one atom selected from a group consisting of a nitrogen atom, a phosphorus atom, and a sulfur atom, and does not include active hydrogen, the monovalent functional group being bonded to R 3 through a nitrogen atom, a phosphorus atom, or a sulfur atom, R 1 and R 2 are a hydrocarbyl group, R 3 is a hydrocarbylene group, and n is an integer from 0 to 2, provided that a plurality of R 1 are either identical or different when a plurality of R 1 are present, and a plurality of R 2 are either identical or different when a plurality of R 2 are present, and wherein A 1 is a nitrogen-containing group in which two hydrogen atoms of a primary amino group are substituted with two protecting groups, a nitrogen-containing group in which one hydrogen atom of a secondary amino group is substituted with one protecting group, an imino group, a pyridyl group, a phosphorus-containing group in which two hydrogen atoms of a primary phosphino group are substituted with two protecting groups, a phosphorus-containing group in which one hydrogen atom of a secondary phosphino group is substituted with one protecting group, a tertiary phosphino group, or a sulfur-containing group in which one hydrogen atom of a thiol group is substituted with one protecting group. a main chain modification step that reacts at least either an unsaturated bond or a functional group that is included in the conjugated diene-based polymer and is not situated at a terminal of the conjugated diene-based polymer, with a specific compound that includes a functional group that interacts with silica, the main chain modification reaction being performed against a terminal-modified polymer or being performed simultaneously with a terminal modification reaction that modifies the terminal of the conjugated diene-based polymer,_the terminal-modified polymer being obtained by introducing a functional group that interacts with silica into at least one terminal of the conjugated diene-based polymer wherein the specific compound is at least one compound selected from a group consisting of a compound (a-1) represented by a formula, and a compound (a-2) that includes a functional group and a group in its molecule, the functional group being at least one functional group selected from a group consisting of a cyclic ether group and a (thio)carbonyl group, and the group including at least one atom selected from a group consisting of a nitrogen atom, a phosphorus atom, an oxygen atom, and a sulfur atom, and not including active hydrogen, the group differing from the functional group, wherein A 1 is a monovalent functional group that includes at least one atom selected from a group consisting of a nitrogen atom, a phosphorus atom, and a sulfur atom, and does not include active hydrogen, the monovalent functional group being bonded to R 3 through a nitrogen atom, a phosphorus atom, or a sulfur atom, R 1 and R 2 are a hydrocarbyl group, R 3 is a hydrocarbylene group, and n is an integer from 0 to 2, provided that a plurality of R 1 are either identical or different when a plurality of R 1 are present, and a plurality of R 2 are either identical or different when a plurality of R 2 are present, and wherein A 1 is a nitrogen-containing group in which two hydrogen atoms of a primary amino group are substituted with two protecting groups, a nitrogen-containing group in which one hydrogen atom of a secondary amino group is substituted with one protecting group, an imino group, a pyridyl group, a phosphorus-containing group in which two hydrogen atoms of a primary phosphino group are substituted with two protecting groups, a phosphorus-containing group in which one hydrogen atom of a secondary phosphino group is substituted with one protecting group, a tertiary phosphino group, or a sulfur-containing group in which one hydrogen atom of a thiol group is substituted with one protecting group.