Suspension and compression coil spring for suspension

A knee action type suspension device (11) is provided with an arm member (20), a coiled compression spring (21), and a shock absorber (24). The arm member (20) is supported by a pivot (31) so as to be capable of pivoting in the vertical direction, the pivot (31) being provided to an arm mounting section (30). The coiled spring (21) is disposed between spring seats (22, 23). The coiled spring (21) extends and retracts between a fully rebound state and a fully bumped state according to the magnitude of a load applied to the vehicle body. The wire (40) of the coiled spring (21) has a large-diameter wire section (40a), a small-diameter wire section (40b), and a wire diameter changing section (40c). The large-diameter wire section (40a) is provided to a first portion (21a) of the coiled spring (21), the first portion (21a) being located on the side of the coiled spring (21) which is closer to the pivot (31). The small-diameter wire section (40b) is provided to a second portion (21b) of the coiled spring (21), the second portion (21b) being located on the side of the coiled spring (21) which is farther from the pivot (31). The wire diameter (d1) of the large-diameter wire section (40a) is greater than the wire diameter (d2) of the small-diameter wire section (40b).