A battery state detection device comprising: a circuit board that detects a current; a casing with a board storage space formed therein, the board storage space storing the circuit board, the casing including an open mouth through which one side of the board storage space is opened; and a lid part that closes the open mouth of the casing, a welded portion being formed along an edge portion of the open mouth, the welded portion being a portion in which the casing and the lid part are connected to each other by welding; a shunt resistor, wherein the circuit board detects a current having flowed through the shunt resistor, the storage space of the casing stores the circuit board, a plurality of anti-rattling pins (56, 57) are provided in the storage space of the casing, each of the anti-rattling pins (56, 57) includes: a tapered portion having a tapered shape, the tapered portion being formed at the distal end of the anti-rattling pin (56, 57), the circuit board has a reception hole (58, 59) that receives the anti-rattling pin (56, 57), characterized by: each of the anti-rattling pins (56, 57) further includes a plurality of crash ribs each having a rib-like shape starting from a position located at a proximal side relative to the tapered portion and extending in a longitudinal direction of the anti-rattling pin (56, 57), wherein each of the crash ribs has a tapered shape that flares out toward the proximal side of the anti-rattling pin (56, 57). a circuit board that detects a current; a casing with a board storage space formed therein, the board storage space storing the circuit board, the casing including an open mouth through which one side of the board storage space is opened; and a lid part that closes the open mouth of the casing, a welded portion being formed along an edge portion of the open mouth, the welded portion being a portion in which the casing and the lid part are connected to each other by welding; a shunt resistor, wherein the circuit board detects a current having flowed through the shunt resistor, the storage space of the casing stores the circuit board, a plurality of anti-rattling pins (56, 57) are provided in the storage space of the casing, each of the anti-rattling pins (56, 57) includes: a tapered portion having a tapered shape, the tapered portion being formed at the distal end of the anti-rattling pin (56, 57), the circuit board has a reception hole (58, 59) that receives the anti-rattling pin (56, 57), a tapered portion having a tapered shape, the tapered portion being formed at the distal end of the anti-rattling pin (56, 57), the circuit board has a reception hole (58, 59) that receives the anti-rattling pin (56, 57), characterized by: each of the anti-rattling pins (56, 57) further includes a plurality of crash ribs each having a rib-like shape starting from a position located at a proximal side relative to the tapered portion and extending in a longitudinal direction of the anti-rattling pin (56, 57), wherein each of the crash ribs has a tapered shape that flares out toward the proximal side of the anti-rattling pin (56, 57). each of the anti-rattling pins (56, 57) further includes a plurality of crash ribs each having a rib-like shape starting from a position located at a proximal side relative to the tapered portion and extending in a longitudinal direction of the anti-rattling pin (56, 57), wherein each of the crash ribs has a tapered shape that flares out toward the proximal side of the anti-rattling pin (56, 57).