The present invention provides a silicon nitride circuit board in which metal plates are attached on front and rear sides of a silicon nitride substrate having a three-point bending strength of 500 MPa or higher, with attachment layers interposed therebetween, wherein assuming that a thickness of the metal plate on the front side is denoted by t1, and a thickness of the metal plate on the rear side is denoted by t2, at least one of the thicknesses t1 and t2 is 0.6 mm or larger, a numerical relation: 0.10 ≤ |t1 - t2| ≤ 0.30 mm is satisfied, and warp amounts of the silicon nitride substrate in a long-side direction and a short-side direction both fall within a range from 0.01 to 1.0 mm. Due to above configuration, TCT properties of the silicon nitride circuit board can be improved even if the thicknesses of the front and rear metal plates are large.