A sensor unit is disclosed which is adapted to be used as a detector for a fuel gauge, an oil pressure gauge or the like for a vehicle. A variable resistor serving as a signal converting device is securely fitted at both ends thereof in board fixing grooves formed at a frame fixed on a fixing bracket, so that fixing of the variable resistor may be accomplished without using adhesives. Fixing and electrical connection of a connection conductor are attained by merely fitting the connection conductor in an extension restraining groove without soldering.