A physical quantity detector, such as a pressure sensor and a load sensor, includes a cylindrical part of which one end is closed with a strain generating part and a sensor part formed on the strain generating part. The cylindrical part is produced by melting an alloying material having a composition capable of yielding an amorphous alloy, injecting the resultant molten alloy into a metal mold, and cooling the molten alloy in the metal mold to confer amorphousness on the alloy. The metal mold includes a split mold having at least two split parts for forming a cavity and an insert pin to be inserted into the cavity so as to define the inner configuration of the cylindrical part, or further an insert core to be inserted into the mold so as to form the surface of the cavity corresponding to the surface of the strain generating part.