Surface treatment agent and method of producing substrate having surface-treated layer

A surface treatment agent, comprising:

• a fluorine-containing compound (A) having a reactive silyl group;
• and
• at least one compound (B) selected from the group consisting of a fluorine-containing ketone compound (B1) represented by the following Formula (B1), a fluorine-containing cyclic ketone compound (B2) represented by the following Formula (B2), and a fluorine-containing polyether compound (B3) represented by the following Formula (B3):
• R1COR2 (B1)
• R4—[OR5]q—R6 (B3)
• wherein in Formula (B1), each of R1 and R2 independently represents a linear, branched, or cyclic fluorine-containing alkyl group having from 1 to 5 carbon atoms,
• in Formula (B2), R3 represents a residue that forms a 3- to 5-membered ring structure with a carbon atom of a carbonyl group and that has a fluorine atom, and R3 may be substituted with a fluorine-containing alkyl group having from 1 to 2 carbon atoms, and
• in Formula (B3), each of R4 and R6 independently represents a fluorine-containing alkyl group having from 1 to 3 carbon atoms, q represents an integer of 1 or more, R5 represents a perfluoroalkylene group having from 1 to 6 carbon atoms, and in a case in which q is an integer of 2 or more, a plurality of R5s may be the same or different.