To provide a high pressure fuel supply pump capable of forming members, in which valve seats of a discharge valve mechanism and relief valve mechanism are formed, by a small member and having a simple seal mechanism at a portion of the members where the valve seat is therein formed and having suitable assembly performance.

A fuel passage in which one end is opened in the center of the valve seat and the other end is opened at the other side of the cylindrical member is arranged on a cylindrical member in which the valve seat is formed on one side, the cylindrical member is inserted into a through-hole formed on a pump housing, and a seal member made of a 4-fluorinated ethylene material is interposed between an outer periphery of the cylindrical member and an inner periphery of the through-hole.