To obtain a photoelectric detector with a cooler having a good thermal bonding property and good assembling workability of a detector and a cooler by connecting a contact part for placing a tip end portion and a cooler of a cathode substrate via a container filling with a low-melting point metal and bonding them through dissolving and, solidifying the low-melting point metal.

When a detector main body 2 is inserted into a glass bulb from a downward direction in a state in which a low-melting point metal holding container 12 filled with a chip-shaped low-melting point metal is held by a groove at a bottom portion of the container 12, the container 12 comes into contact with a top board 14a having a contact portion with its thermal conductivity and electrical insulation property adhered and fixed to an upper end of the glass bulb 1 and inserted into the container 12, and the contact part is inserted into the container 12. When, in this state, the low-melting point metal is solidified after heated and dissolved a bonding piece 5A and the top board 14a are bonded with each other. A cooler 21 is placed on the top board 14a. Thus, thermal bonding property and assembling workability with the detector main body and the cooler are improved.