The present invention provides a synthetic resin cap capable of providing excellent tamper evidence performance, achieving both sealing performance and opening performance, and securing leak prevention of contents in the container before breakage of the bridges.The present invention includes a top wall, a skirt wall, and a tamper evidence band connected to the skirt wall with bridges interposed therebetween, wherein an inner face of the top wall is provided with an annular inner leg, an annular projection, and an annular outer leg, which are integrally formed, and in the inner leg, a thickness of a transverse section of the intermediate part is substantially constant in a vertical direction, an inner circumferential face and an outer circumferential face of the intermediate part are curved faces that have substantially the same curvature of longitudinal section and are arcuate that are convex inwardly in a radial direction, and an outer circumferential face of a distal end part of the inner leg is provided with a guide face that guides the container mouth part, and the intermediate part is inclined outwardly in the radial direction so that an upper end of the guide face is shifted inwardly in radial direction by 0.1 to 0.6 mm when the inner leg is inserted in the container mouth part.